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Export Query to Text for Oracle Standard


Registry Defragmenter 8.9 Cracked Version

2 Data Pump Export - Oracle Newest Questions - Database Administrators Stack Exchange Oracle Tips and Tricks of the Week Part 2 - Akadia

Using UTL_TCP to send E-Mail from PL/SQL with Oracle 8.1.6

The UTL_TCP is a TPC/IP package that provides PL/SQL procedures to support simple TCP/IP-based communications between servers and the outside world. It is used by the SMTP package, to implement Oracle server-based clients for the internet email protocol. For more information see: Oracle8i Supplied PL/SQL Packages Reference Release 2 (8.1.6).

The following procedure SEND_MAIL can be used to send an E-Mail directly from the database.

CREATE OR REPLACE PROCEDURE send_mail (
  msg_from    varchar2 := 'martin dot zahn at akadia dot ch',
  msg_to      varchar2 := 'martin dot zahn at akadia dot ch',
  msg_subject varchar2 := 'Message from PL/SQL daemon',
  msg_text    varchar2 := 'Automatically send by PL/SQL daemon')
IS
  conn          utl_tcp.connection;
  rc            integer;
  mailhost      varchar2(30) := 'rabbit.akadia.com';
BEGIN
  conn := utl_tcp.open_connection(mailhost,25); -- open the SMTP port
  dbms_output.put_line(utl_tcp.get_line(conn, TRUE));
  rc := utl_tcp.write_line(conn, 'HELO '||mailhost);
  dbms_output.put_line(utl_tcp.get_line(conn, TRUE));
  rc := utl_tcp.write_line(conn, 'MAIL FROM: '||msg_from);
  dbms_output.put_line(utl_tcp.get_line(conn, TRUE));
  rc := utl_tcp.write_line(conn, 'RCPT TO: '||msg_to);
  dbms_output.put_line(utl_tcp.get_line(conn, TRUE));
  rc := utl_tcp.write_line(conn, 'DATA'); -- Start message body
  dbms_output.put_line(utl_tcp.get_line(conn, TRUE));
  rc := utl_tcp.write_line(conn, 'Subject: '||msg_subject);
  rc := utl_tcp.write_line(conn, '');
  rc := utl_tcp.write_line(conn, msg_text);
  rc := utl_tcp.write_line(conn, '.');  -- End of message body
  dbms_output.put_line(utl_tcp.get_line(conn, TRUE));
  rc := utl_tcp.write_line(conn, 'QUIT');
  dbms_output.put_line(utl_tcp.get_line(conn, TRUE));
  utl_tcp.close_connection(conn);    -- Close the connection
EXCEPTION
  when others then
    raise_application_error(-20000,
    'Unable to send E-mail message from pl/sql procedure');
END;
/

Examples

set serveroutput on
exec send_mail();
exec send_mail(msg_to  =>'martin dot zahn at akadia dot ch');
exec send_mail(msg_to  =>'martin dot zahn at akadia dot ch',
               msg_text=>'How to send E-Mail from PL/SQL');

Show Oracle Version and installed Options

The data dictionary views V$OPTION and V$VERSION can be used to get the current Oracle version and the installed options. Click here for the Script.

select banner
from   sys.v$version;

select parameter
from   sys.v$option
where  value = 'TRUE';

select parameter
from   sys.v$option
where  value <> 'TRUE';

begin
    dbms_output.put_line('Specific Port Information:
    '||dbms_utility.port_string);
end;
/

Here is the produced Output from the Script:

Oracle Version:

BANNER
----------------------------------------------------------------
Oracle8i Enterprise Edition Release 8.1.5.0.0 - Production
PL/SQL Release 8.1.5.0.0 - Production
CORE Version 8.1.5.0.0 - Production
TNS for 32-bit Windows: Version 8.1.5.0.0 - Production
NLSRTL Version 3.4.0.0.0 - Production

Installed Options:

PARAMETER
----------------------------------------------------------------
Objects
Advanced replication
Bit-mapped indexes
Connection multiplexing
Connection pooling
Database queuing
Incremental backup and recovery
Instead-of triggers
Parallel backup and recovery
Parallel execution
Parallel load
Point-in-time tablespace recovery
Fine-grained access control
N-Tier authentication/authorization
Function-based indexes
Plan Stability
Online Index Build
Coalesce Index
Managed Standby
Materialized view rewrite
Materialized view warehouse refresh
Database resource manager
Spatial
Visual Information Retrieval
Export transportable tablespaces
Transparent Application Failover
Fast-Start Fault Recovery
Sample Scan
Duplexed backups
Java

Not Installed Options:

PARAMETER
----------------------------------------------------------------
Partitioning
Parallel Server

Specific Port Information: IBMPC/WIN_NT-8.1.0

Oracle 8i temporary Tables

A temporary table has a definition or structure that persists like that of a regular table, but the data it contains exists only for the duration of a transaction or session. Oracle8i allows you to create temporary tables to hold session-private data. You specify whether the data is specific to a session or to a transaction.

There are two options: Delete rows after commit or Delete rows after exit session.

create global temporary table mytemp (a date)
  on commit delete rows -- Delete rows after commit
/

Show Status of the temporary table

select table_name, temporary, duration
  from user_tables
 where table_name = 'MYTEMP
/

Rows exists after insert

insert into mytemp values (sysdate);
select from mytemp;

Inserted rows are missing after commit

commit;
select from mytemp;

Avoid REVERSE KEY index together with a FOREIGN Key

This alert comes from the oracle support.

Reverse key index on foreign key column allows deletion of parent key !

The FOREIGN KEY integrity constraint is provided to define and ensure the integrity of a parent-child relationship between two tables. It requires that each value in a column, or a set of columns match a value in a related (parent) table's UNIQUE or PRIMARY KEY. FOREIGN KEY integrity constraints also define referential integrity actions such as ON DELETE CASCADE which specifies that upon the deletion of the row in the parent table, all corresponding rows in the referential (child) tables will be deleted as well. If the ON DELETE CASCADE option is not specified for the FOREIGN KEY constraint, the deletion of the row from the parent table is prevented with an error message signalling the presence of corresponding rows in a child table.

If, however, a REVERSE KEY index is created on the column(s) defined in the FOREIGN KEY integrity constraint, the deletion of the row in the parent table is allowed to proceed without error, thereby leaving orphaned rows in the corresponding child table(s). If the FOREIGN KEY was created with the ON DELETE CASCADE option, this directive is ignored and the corresponding rows in the child table are not deleted. 

Likelihood of Occurence

If you have defined a REVERSE KEY index on column(s) designated as a FOREIGN KEY constraint and have deleted rows from the parent table, then it is likely that you will have orphaned rows in the child table.

There are no error messages generated unless you disable and attempt to re-enable the FOREIGN KEY constraint. If orphaned rows exist in the child table, you will receive an ORA-02291 error message listing the name of the FOREIGN KEY constraint. "ORA-02291:integrity constraint (SCOT7.FK-DEPTNO),violated-parent key not found"

Inserting in two or more tables with SQLLoader

If you want to load data from an ASCII or EBCDIC file into an Oracle Database -- SQLLoader is the tool. In this article we want to show, how to distribute the rows in the file in two tables depending on a value at a specified character position in the file. 
As an example, insert the row in table A if the value ra is 2 on position 7, insert the row in table B if ra is 1 (see the following figure).

You need the following SQLLoader controlfile to accomplish this task.

OPTIONS (SKIP=1)
LOAD DATA
CHARACTERSET WE8EBCDIC500
INFILE '$BOTENFILE' "fix 86"
BADFILE '$BOTENFILE.bad'
DISCARDFILE '$BOTENFILE.dsc'
REPLACE
INTO TABLE B
WHEN ra = X'F1'
(
  astrnr   POSITION (1:6)    INTEGER EXTERNAL,
  ra       POSITION (7:7)    INTEGER EXTERNAL,
  mc       POSITION (8:8)    INTEGER EXTERNAL,
  astrg    POSITION (9:36)   CHAR,
  astrgk   POSITION (37:61)  CHAR "UPPER(LTRIM(RTRIM(:astrgk)))",
  astamm   POSITION (62:71)  CHAR,
  aadrplz  POSITION (72:77)  INTEGER EXTERNAL,
  astrart  POSITION (78:79)  INTEGER EXTERNAL,
  apra     POSITION (80:81)  INTEGER EXTERNAL,
  asprc    POSITION (82:82)  INTEGER EXTERNAL,
  gplz     POSITION (83:86)  INTEGER EXTERNAL,
  line     SEQUENCE (1,1)
)
INTO TABLE A
WHEN ra = X'F2'
(
  astrnr   POSITION (1:6)    INTEGER EXTERNAL,
  ra       POSITION (7:7)    INTEGER EXTERNAL,
  abzart   POSITION (8:8)    INTEGER EXTERNAL,
  abbez    POSITION (9:11)   CHAR "(LTRIM(RTRIM(:abbez)))",
  ahnrvn   POSITION (12:15)  INTEGER EXTERNAL,
  ahnrva   POSITION (16:17)  CHAR "(LTRIM(RTRIM(:ahnrva)))",
  ahnrbn   POSITION (18:21)  INTEGER EXTERNAL,
  ahnrba   POSITION (22:23)  CHAR "(LTRIM(RTRIM(:ahnrba)))",
  atc      POSITION (24:24)  CHAR,
  line     SEQUENCE (1,1)
)

The first line in the EBCDIC file is skipped OPTIONS (SKIP=1). The most interesting part is the WHEN clause. The attribute "ra" is the single character that has the value specified by hex-byte in the character encoding schema, such as X ' F1 '  (equivalent to 241 decimal), "X" must be uppercase. Due to National Language Support NLS requirements, hex 00 cannot be used (See Oracle 8 Utilities Guide).

Avoid Rollback Segement Problems with huge Updates / Deletes

If you have to UPDATE or DELETE a huge number of rows, you may encounter problems with Rollback Segmets. One solution is to COMMIT after sets of n Rows, as the next example shows.

declare
  i number := 0;
  n numner := 1000;
  --
  -- Lock the Rows for the UPDATE
  --

  cursor s1 is SELECT FROM tab1
                WHERE col1 = 'value1'
                  FOR UPDATE;
begin
  for c1 in s1 loop
      update tab1 set col1 = 'value2'
             where current of s1;
      --
      -- Commit after every n rows
      --

      i := 1 + 1;
      if i > n then
         commit;
         i := 0;
      end if;
  end loop;
  commit;
end;
/

Special characters needs 2 bytes in UTF8

If you want to import a dump file created by e.g. WE81SO8859P1 character set into UTF8 you can get an ORA-1401 Truncating Data Too Long for a Column. You can prevent this message by increasing the size of your VARCHAR2 fields, because a special character like umlauts needs 2 bytes in UTF8 and e.g. one byte in WE81SO8859P1. This means that you must resize all your VARCHAR2 fields if you want to import VARCHAR2 fields with umlauts.

How to set SYS password  in Oracle for NT ?

  • Check where your password file is located

  1. Run the Windows NT Registry editor regedt32

  2. Make the HKEY_LOCAL_MACHINE window of the Registry editor the active window.
    In the tree view, open the Software folder, then the ORACLE folder.

  3. The correct location of the password file for each database appears in the right-hand pane of the Registry editor. The format appears as ORA_<SID>_PWFILE, followed by the password file location where <SID> is the name of the Oracle database or the standard folder $ORACLE_HOME/database filename PWD<SID>.ora

  • Rename your old PWD<S ID>. ora file

  • Create a new password file with orapwd.exe

orapwd file=<fname> password=<password> entries=<users>

where: 

file name of password file (mand)
password password for SYS and INTERNAL (mand)
entries maximum number of distinct DBA and OPERs (opt)

There are no spaces around the equal-to (=) character, e.g.

orapwd file=passwd.ora password=manager entries=10

After you have created the password file, you can relocate it as you choose. After relocating the
password file, you must reset the appropriate environment variables to the new pathname (check ORA_<SID>_PWFILE in registry), reboot your machine. If you receive the file full error (ORA-1996) when you try to grant SYSDBA or SYSOPER system privileges to a user, you must create a larger password file and re-grant the privileges to all of the users. In 8.1.5 the str<SID>.cmd file doesn't exist anymore and just one service handle all database actions, like
Automatic startup, shutdown, pfile, etc.

How to avoid having remaining characters filled with blanks?

You are spooling a file with SQLPLUS and want to avoid having remaining characters filled with blanks or tabs. This may happen if you have set LINESIZE 500 and your table rows are only 100 in size. The resulting script will not have the correct format although the display on the screen will look correct. Another situation when this may happen is if you are dumping a table to a comma delimited ASCII file to be used with SQL LOADER. The line length is likely to be padded with blanks and will dramatically increase the size of the file. Use the TRIMSPOOL ON command at the beginning of your SQL script. This will trim the unneeded spaces in your file.

How to split Export or standard output into smaller pieces ?

If you want to export the whole oracle database, or create a TAR archive of one of your filesystem, you may reach a filesize which is bigger than 2 GB. On some unix filesystems this is the maximal size for one single file. Or you want to distribute your software release over the internet, then you usually create a TAR file which can be downloaded. For your customers it may be helpful to download several small chunks than one huge file. To accomplish these tasks you need split and often a named pipe.

  1. Create a named pipe
    mknod tar_pipe p
      

  2. Write to the named pipe as the first process
    tar cvf tar_pipe <tar_directory> &
      

  3. Read from the named pipe as the second process
    split -b 100k tar_pipe tar_split_
    Now you have several files
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_aa
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_ab
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_ac
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_ad
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_ae
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_af
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_ag
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_ah
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_ai
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_aj
    -rw-r--r-- 1 root root 102400 Apr 24 12:10 tar_split_ak
      

  4. Concatenate the files and recreate tar_directory
    cat tar_split_ | tar xvf -

  1. Create a named pipe
    mknod export_pipe p
      

  2. Read from the named pipe as the first process
    split -b 100k export_pipe full_export_ &
      

  3. Export to the named pipe
    exp userid=system/... full=y file=export_pipe
    rm
    export_pipe
      

  4. Import the database again
    mknod import_pipe p
    cat full_export_ > import_pipe &
    imp userid=system/... full=y file=import_pipe
    rm import_pipe

How to remove the default value from a column ?

If you want to remove the default value for a column which already has a default value, use the following two equivalent statements in Oracle8i (Note: in Oracle 7/8 they are not equivalent).

ALTER TABLE address MODIFY (name DEFAULT NULL);
ALTER TABLE address MODIFY (name VARCHAR2(20) DEFAULT NULL);

Create table ADDRESS, then set a default value for column NAME.

CREATE TABLE address (
  id   NUMBER(5),
  name VARCHAR2(20)
);

ALTER TABLE address MODIFY (name VARCHAR2(20) DEFAULT 'Unknown');

Check the default value in the data dictionary

COLUMN  column_name FORMAT A10
COLUMN  data_default FORMAT A10
SELECT column_name,
       data_default,
       data_length
 FROM user_tab_columns
WHERE table_name = 'ADDRESS';

COLUMN_NAM DATA_DEFAU DATA_LENGTH
---------- ---------- -----------
ID                             22
NAME       'Unknown'           20

Remove default value and check again

ALTER TABLE address MODIFY (name DEFAULT NULL);

COLUMN_NAM DATA_DEFAU DATA_LENGTH
---------- ---------- -----------
ID                             22
NAME       NULL                20

ALTER TABLE address MODIFY (name VARCHAR2(20) DEFAULT NULL);

COLUMN_NAM DATA_DEFAU DATA_LENGTH
---------- ---------- -----------
ID                             22
NAME       NULL                20

The table USER_TAB_COLUMNS show a NULL string irrespective of weather a datatype is specified in the table modify statement or not. In Oracle7 and 8 a blank null is stored when you use ALTER TABLE address MODIFY (name DEFAULT NULL);

How to avoid performance disaster with PL/SQL tables ?

Last week, we have been called to verify an application written in PL/SQL, with a poor performance and a lot of CPU consuming. The application fetches about 100'000 rows from the database into a PL/SQL table for further processing. The PL/SQL table fits completely into the memory, no swapping takes place. A closer look shows, that for each processing cycle a procedure was called with the PL/SQL table as an argument -- here we found the performance disaster -- in PL/SQL arguments are passed by value, that means, the whole table was copied for each cycle !

First, we want to show a small example (Example 1) with this performance bottleneck -- DO NOT USE IT IN YOUR APPLICATION -- it's just a demonstration. Next we will show you, how to avoid this situation in Oracle7/8 (Example 2) and at last we will show you the NOCOPY hint in Oracle8i (Example 3).

The Procedure run_local uses local declaration of table emp_tab. For each call of process_local, the full table emp_tab will be copied to the procedure and return after processing (IN OUT definition), the content of the table could be changed. Never do it in that way !

The procedure run_global uses global declaration of table emp_tab. The procedure
uses the global definition of emp_tab, therefore no argument passing is necesary. This procedure runs much faster, but we do not like like global variables ...

CREATE OR REPLACE
PACKAGE BODY plsql_tab IS
  --
  TYPE tab_type IS TABLE OF emp%ROWTYPE
    INDEX BY BINARY_INTEGER;
  g_emp_tab tab_type;
  --
  NofRuns CONSTANT NUMBER := 10;
  NofRecords CONSTANT NUMBER := 9999;
  --
  -- Local usage
  -- 

  PROCEDURE process_local (p_emp_tab IN OUT tab_type) IS
    -- Parameter p_emp_tab is defined as IN OUT, 
    -- table emp_tab could be changed

    i BINARY_INTEGER;
    BEGIN
    -- Parse EMP table

    i := p_emp_tab.FIRST;
    IF (NOT i IS NULL) THEN
      LOOP
        -- Do something ...
        dbms_output.put(p_emp_tab(i).empno);
        dbms_output.put_line('  ' || p_emp_tab(i).ename);
        -- Get next record
        i := p_emp_tab.NEXT(i);
        EXIT WHEN (i IS NULL);
      END LOOP;
    END IF;
  END;
  --
  PROCEDURE run_local IS
    l_emp_tab tab_type;
    l_emp_rec emp%ROWTYPE;
  BEGIN
    -- Initialize local table
    FOR i IN 1 .. NofRecords LOOP
      l_emp_rec.empno := i;
      l_emp_rec.ename := 'NEW';
      l_emp_tab(i) := l_emp_rec;
    END LOOP;
    -- Process local table, for each cycle the PL/SQL table is
    -- put and fetch on the argument stack

    FOR i IN 1 .. NofRuns LOOP
      process_local (l_emp_tab);
    END LOOP;
  END; 
  --
  -- Global usage
  --

  PROCEDURE process_global IS
    i BINARY_INTEGER;
  BEGIN
    -- Parse EMP table
   i := g_emp_tab.FIRST;
   IF (NOT i IS NULL) THEN
     LOOP
       -- Do something ...
        dbms_output.put(g_emp_tab(i).empno);
        dbms_output.put_line('  ' || g_emp_tab(i).ename);
      -- Get next record
      i := g_emp_tab.NEXT(i);
      EXIT WHEN (i IS NULL);
    END LOOP;
  END IF;
  END;
  --
  PROCEDURE run_global IS
    -- Use g_emp_tab (global definition)
    l_emp_rec emp%ROWTYPE;
  BEGIN
    -- Initialize global table
    FOR i IN 1 .. NofRecords LOOP
      l_emp_rec.empno := i;
      l_emp_rec.ename := 'NEW';
      g_emp_tab(i) := l_emp_rec;
    END LOOP;
    -- Process global table

    FOR i IN 1 .. NofRuns LOOP
      process_global;
    END LOOP;
  END; 
  --
END plsql_tab;
/

When the parameters hold large data structures, all this copying slows down execution and uses up memory. To prevent that, you can specify the NOCOPY hint in Oracle8i, which allows the PL/SQL compiler to pass OUT and IN OUT parameters by reference. Remember, NOCOPY is a hint, not a directive.

DECLARE
  TYPE Numlist IS TABLE OF emp.empno%TYPE;
  Id Numlist;
  PROCEDURE GetEmp (pDeptNo IN NUMBER, pId OUT NOCOPY Numlist) IS
  BEGIN
    SELECT empno BULK COLLECT INTO pId
     FROM emp
    WHERE deptno = pDeptNo;
  END;
BEGIN
    GetEmp(10,Id);
    FOR i IN Id.FIRST..Id.LAST LOOP
      dbms_output.put_line(Id(i));
    END LOOP;
END;
/

Speed up your transactions with PL/SQL tables

Datawarehouse Applications often process several millions rows, often each record is selected, processed and updated again in the database. This can be a very time consuming task. If you can split to whole transaction in smaller pieces and your machine have enough physical memory use PL/SQL tables, which are kept in-memory. Select all needed rows and insert them into the in-memory PL/SQL table. Then analyze, group or process them directly in the memory, finally write back the whole PL/SQL table to the databse.

In one of our DSS application, we used this approach, the performance gain is incredible. 20'000 records has been processed 100 - 150 times faster with PL/SQL than the direct method (each record separate from / to the database). One further advantage is, that the transaction is less longer open. One disadvantage of PL/SQL tables is, that you have to use one BINARY INTEGER as the key for the table, real primary keys cannot be used in PL/SQL tables. Therefore you have to create an artificial key, based on the real primary key.

To demonstrate this performance gain, we use a simple SELECT, PROCESS, UPDATE transaction, first processing row by row, then using a PL/SQL table.

--
-- PL/SQL-Update
--

SET SERVEROUTPUT ON;
--
DECLARE
  CURSOR check_reload_cur (p_dst_id statreload.dst_id%TYPE) IS
  SELECT 'X'
    FROM statreload
   WHERE dst_id = p_dst_id;
  --
  NofRecords CONSTANT NUMBER := 20000;
  NofKeys    CONSTANT NUMBER := 500;
  --
  hashKey NUMBER(15);
  i NUMBER(15);
  l_dummy CHAR(1);
  --
BEGIN
  -- Clear table STATRELOAD
  DELETE FROM statreload;
  -- Process records
FOR i IN 1..NofRecords LOOP
  BEGIN
     hashKey := MOD(i, NofKeys);
     -- If record has already processed update
     -- the result, else insert it.

     OPEN check_reload_cur (hashKey);
     FETCH check_reload_cur INTO l_dummy;
     IF (check_reload_cur%FOUND) THEN
     UPDATE statreload SET
       sum_weekday = sum_weekday + hashKey,
       sum_weekend = sum_weekend + hashKey,
       num_weekday = num_weekday + 1,
       num_weekend = num_weekend + 1
     WHERE dst_id = hashKey;
   ELSE
     INSERT INTO statreload (
         day, tim_id, chl_id, csh_id, dst_id, srv_id, rld_id,
         sum_weekday, sum_weekend, num_weekday,
          num_weekend, trusted
   ) VALUES (
     TRUNC(SYSDATE), 1, 1, 1, hashKey, 1, 1,
     hashKey, hashKey, 1, 1, 0);
     END IF;
      CLOSE check_reload_cur;
  END;
END LOOP;
  COMMIT;
END;
/

--
-- PL/SQL-Tabelle
--

SET SERVEROUTPUT ON;
--
DECLARE
  TYPE t_reload IS TABLE OF statreload%ROWTYPE
    INDEX BY BINARY_INTEGER;

  tab_reload t_reload;
  --
  NofRecords CONSTANT NUMBER := 20000;
  NofKeys    CONSTANT NUMBER := 500;
  --
  hashKey NUMBER(15);
  i NUMBER(15);
  --
BEGIN
  -- Process records
FOR i IN 1..NofRecords LOOP
  BEGIN
      hashKey := MOD(i, NofKeys);
      IF (tab_reload.EXISTS(hashKey)) THEN
        -- Update temp. table
        tab_reload(hashKey).sum_weekday :=
           tab_reload(hashKey).sum_weekday + hashKey;
        tab_reload(hashKey).sum_weekend :=
           tab_reload(hashKey).sum_weekend + hashKey;
        tab_reload(hashKey).num_weekday :=
           tab_reload(hashKey).num_weekday + 1;
        tab_reload(hashKey).num_weekend :=
           tab_reload(hashKey).num_weekend + 1;
      ELSE
        -- Insert temp. table
        tab_reload(hashKey).sum_weekday := hashKey;
        tab_reload(hashKey).sum_weekend := hashKey;
        tab_reload(hashKey).num_weekday := 1;
        tab_reload(hashKey).num_weekend := 1;
      END IF;
  END;
END LOOP;
  -- Clear table STATRELOAD
  DELETE FROM statreload;
  -- Insert into table STATRELOAD
  i := tab_reload.FIRST;
  IF (NOT i IS NULL) THEN
    LOOP
   INSERT INTO statreload (day, tim_id, chl_id, 
       csh_id, dst_id, srv_id, rld_id, sum_weekday, 
       sum_weekend, num_weekday, num_weekend, trusted)
    VALUES (TRUNC(SYSDATE), 1, 1, 1, i, 1, 1, 
      tab_reload(i).sum_weekday,
      tab_reload(i).sum_weekend,
      tab_reload(i).num_weekday,
      tab_reload(i).num_weekend,0);
      i := tab_reload.NEXT(i);
      EXIT WHEN (i IS NULL);
    END LOOP;
  ELSE
  dbms_output.put_line('No records to update!');
  END IF;
  COMMIT;
END;
/

How to migrate LONG fields into VARCHAR2

In Oracle7 the LONG datatype often cause difficulties, for example a table in Oracle7 can have only one LONG, LONG's couldn't replicated and more. We have seen, that in many cases simple text is inserted in these LONG fields. Due to this, we suggest to convert the LONGs into VARCHAR2 with the following simple PL/SQL script. In Oracle8 you may specify a longer VARCHAR2 (40000).

CREATE TABLE long_tab (
long_field   LONG
);

ALTER TABLE long_tab ADD (char_field VARCHAR2(2000));

CREATE OR REPLACE PROCEDURE long2varchar IS
  CURSOR getrowid IS
  SELECT rowid, long_field
    FROM long_tab;
BEGIN
  FOR rec IN getrowid LOOP
    UPDATE long_tab
    SET char_field = rec.long_field;
  END LOOP;
  COMMIT;
END;
/

EXECUTE long2varchar;

Tracing other user sessions

If you want to look or trace at a certain oracle process, belonging to an Orcale User, the best way is to trace the session for this user. As a DBA, you can trace other sessions, normal users can only trace their own sessions. 

1). Enable TIMED statistics

ALTER SESSION SET TIMED_STATISTICS = TRUE;

However, most Oracle systems have this INIT.ORA parameter already set to TRUE, because the performance loss is small.

2). Get SID and Serial#

SELECT s.sid,s.serial#,p.pid,p.program
  FROM v$session s, v$process p
WHERE s.paddr = p.addr;

3). Stop the process

EXEC dbms_system.sql_trace_in_session(sid,serial,true);

Then use TKPROF in USER_DUMP_DEST with the generated trace file.

How to start an Oracle database with corrupted or lost dbfile ?

Help -- we cannot start the Oracle Database ... we get an error message telling us, that one datafile is lost or corrupted ... what can we do ?

ORA-01157: cannot identify/lock data file 10 - see DBWR trace file
ORA-01110: data file 10: '/u01/db/test.dbf'

If the database is in ARCHIVELOG mode with a working online backup concept you are a lucky person, recover the database and everything is OK. But what can we do, if the database is in NOARCHIVELOG mode and no backup is present ?

1). Switch the damaged datafile to the RECOVER status

svrmgr> ALTER DATABASE DATAFILE '/u01/db/test.dbf' OFFLINE DROP;
svrmgr> SELECT file#,status,bytes,name FROM v$datafile;
  FILE# STATUS       BYTES NAME
------- -------- --------- ------------------------------
      1 SYSTEM   104857600 /u01/db/SOL3/sys/SOL3_sys1.dbf
      2 RECOVER    2097152 /u01/db/test.dbf

2). Stop and Start the database to verify that the database can be started without ' test.dbf '.

svrmgr> SHUTDOWN IMMEDIATE;
svrmgr> STARTUP;

3). DROP the tablespace to which the datafile belongs

svrmgr> DROP TABLESPACE test INCLUDING CONTENTS;

The database can only be stopped with SHUTDOWN ABORT with a damaged or lost datafile and the datafile is still in ONLINE mode. Therefore it's better to switch the datafile to the RECOVER status as shown above before stopping the database. However there is a way to switch the datafile to the RECOVER status when the database is stopped.

1). Mount the database and switch the damaged datafile to the RECOVER status

svrmgr> STARTUP MOUNT;
svrmgr> ALTER DATABASE DATAFILE '/u01/db/test.dbf' OFFLINE DROP;
svrmgr> ALTER DATABASE OPEN;

2). DROP the tablespace to which the datafile belongs

svrmgr> DROP TABLESPACE test INCLUDING CONTENTS;

3). Stop and Start the database to verify that the database can be started without ' test.dbf '.

svrmgr> SHUTDOWN IMMEDIATE;
svrmgr> STARTUP;

  • The term ' OFFLINE DROP ' is misleading, it is not possible to drop a datafile with this command. The only purpose of this command is to startup a database with damaged or missing datafile and the databae is in NOARCHIVELOG mode.

  • The command ' ALTER DATABASE DATAFILE ... OFFLINE DROP ' changes the datafile status from ONLINE to RECOVER. In this mode, the database can be started even if the datafile is not present.

  • If space management (e.g. CREATE TABLE ..) occurs for this datafile, Oracle will try to allocate space in this ' dropped ' datafile and fails.

  • The only way to drop a datafile is to drop the tablespace to which the datafile belongs. Unfortunately you will lose data if you don't have an actual backup.

How to drop a tablespace containing tables with references ?

You cannot drop a tablespace containing tables with active referential integrity constraints.

SQL> DROP TABLESPACE test1 INCLUDING CONTENTS;
ORA-02449: unique/primary keys in table referenced by foreign keys

Before you can drop the tablespace you have to to drop or disable the referential integrity constraints. You can verify the tables with references to tables in other tablespaces.
Let's create an example.

CREATE TABLESPACE test1 datafile '/u01/db/test1.dbf' SIZE 2M REUSE;
CREATE TABLESPACE test2 datafile '/u01/db/test2.dbf' SIZE 2M REUSE;

CREATE TABLE test1 (
  id1    NUMBER(5)   PRIMARY KEY,
  val    VARCHAR2(10)
)
TABLESPACE test1;

CREATE TABLE test2 (
  id2    NUMBER(5)   PRIMARY KEY,
  id1    NUMBER(5)   REFERENCES test1 (id1),
  val    VARCHAR2(10)
)
TABLESPACE test2;

SQL> ALTER TABLESPACE test1 OFFLINE;
SQL> DROP TABLESPACE test1 INCLUDING CONTENTS;
ORA-02449: unique/primary keys in table referenced by foreign keys

List the Primary- and Foreign Key Relationsships. The output of the SQL-Statement is listed below, click here for the SQL-Statement.

                 From      From    To       To
Table            Foreign   Foreign Primary  Primary
Owner Tablespace Table     Column  Table    Column
----- ---------- -------- ------- -------- ----------
SCOTT TAB        EMP       DEPTNO  DEPT     DEPTNO
      TAB        EMP       MGR     EMP      EMPNO
      TAB        ITEM      ORDID   ORD      ORDID
      TAB        ORD       CUSTID  CUSTOMER CUSTID
      TAB        ORD       CUSTID  CUSTOMER CUSTID
      TEST1      TEST2     ID1     TEST1    ID1

SELECT constraint_name,table_name
  FROM dba_constraints
WHERE constraint_type = 'R'
   AND table_name like upper ('%TEST%');

CONSTRAINT_NAME                 TABLE_NAME
------------------------------ ------------------------------
SYS_C005395                     TEST2

SQL> ALTER TABLE test2 DROP CONSTRAINT SYS_C005395;

SQL> DROP TABLESPACE test1 INCLUDING CONTENTS;

How to load EBCDIC data into an Oracle database  ?

Last week, we had to load EBCDIC data from an IBM host the an Oracle 8 Database. Well, not a job we are doing every day, but with some hints from the Oracle Support an easy task.

The "dd" Unix command can be used to convert EBCDIC data files to ASCII and vice-versa.
For example:

dd if=data.ebc of=data.asc conv=ascii cbs=87

The example takes data.ebc as EBCDIC input file with a fixed record length of 86, converts it into ASCII, and writes the converted output to file data.asc.

Specify the Characterset WE8EBCDIC500 for the EBCDIC data. The following example shows the SQLLoader Controlfile to load a fixed length EBCDIC record into the Oracle Database.

LOAD DATA
CHARACTERSET WE8EBCDIC500
INFILE data.ebc "fix 86 buffers 1024"
BADFILE data.bad'
DISCARDFILE data.dsc'
REPLACE
INTO TABLE temp_data
(
  field1    POSITION (1:4)     INTEGER EXTERNAL,
  field2    POSITION (5:6)     INTEGER EXTERNAL,
  field3    POSITION (7:12)    INTEGER EXTERNAL,
  field4    POSITION (13:42)   CHAR,
  field5    POSITION (43:72)   CHAR,
  field6    POSITION (73:73)   INTEGER EXTERNAL,
  field7    POSITION (74:74)   INTEGER EXTERNAL,
  field8    POSITION (75:75)   INTEGER EXTERNAL,
  field9    POSITION (76:86)   INTEGER EXTERNAL
)

 How to show column and table comments ?

If you have to verify an unkown database schema, it can be very helpful to list the table and column comments, specially if there is no documentation. Unfortunately, some designers are too lazy to specify these comments using the following SQL statement:

COMMENT ON TABLE emp IS 'Employee Information';
COMMENT ON COLUMN emp.empno IS 'Employee Identification';

To generate a report with all column and table comments, you can use the following simple SQLPlus script -- click here to show the script.

The script generates the following output:

Table Comments

Table Table
Owner Name                  Comments
----- --------------------- ---------------------------------------
SOL   PRICE                 A group of valid prices connections
      RATE                  Named rates that are applicable
Column Comments on Tabelle: PRICE

Table Column
Owner Name                  Comments
----- --------------------- ---------------------------------------
SOL   NAME                  Name of the priceplan (UNIQUE)
      DESCRIPTION           Description of the priceplan

The Mistery of Inline Views

One of the hidden features of Oracle, are the so called Inline Views (Immediate View, View on the Fly, Anonymous View). They are very useful to overcome some restrictions as:

  • Users want to use Views, but have no CREATE VIEW privilege.
  • A SELECT statement within CONNECT BY can select only one table.

Instead to create a view with CREATE VIEW, which needs the necessary privileges, you can specify the view directly within the FROM clause. The following example, shows how to print the number of rows from two tables in one line using an Inline View.

SELECT e.emp_count, d.dept_count
  FROM (SELECT COUNT() emp_count FROM emp) e,
       (SELECT COUNT() dept_count FROM dept) d;

EMP_COUNT DEPT_COUNT
--------- ----------
       14          4

Another example using an Inline View gives departments' total employees and salaries as a decimal value of all the departments:

SELECT a.deptno "Department",
       (a.num_emp/b.total_count)100 "%Employees",
       (a.sal_sum/b.total_sal)100 "%Salary"
  FROM (SELECT deptno, COUNT() num_emp, SUM(SAL) sal_sum
          FROM emp
        GROUP BY deptno) a,
       (SELECT COUNT() total_count, SUM(sal) total_sal
          FROM emp) b;

Department %Employees   %Salary
---------- ---------- ---------
        10  21.428571 30.146425
        20  35.714286   37.4677
        30  42.857143 32.385874

The next example demonstrates how to overcome the restriction, that a SELECT statement with a CONNECT BY to represent hierarchical dependencies, can specify only one table in the FROM clause. There is no possibility to enter a JOIN directly in the FROM clause. This problem can be solved with an Inline View. In the top SELECT list, all attributes must be defined, including those within the Inline View.

COLUMN employee FORMAT A12 HEADING "Chart"
COLUMN empno    FORMAT 9999 HEADING "EmpNo"
COLUMN job      FORMAT A10 HEADING "Job"
COLUMN dname    FORMAT A10 HEADING "Dept"
COLUMN mgr      FORMAT A8 HEADING "Boss"
COLUMN sal      FORMAT 9999 HEADING "Salary"
COLUMN mgrno    FORMAT A6 HEADING "BossNo"

SELECT employee, empno, job, d.dname, mgr, sal, mgrno
  FROM dept d,
       (SELECT LPAD(' ',2(LEVEL-1)) || ename employee,
               empno, job, deptno, PRIOR(ename) mgr, sal,
               DECODE(LEVEL,1,NULL,PRIOR(empno)) mgrno
          FROM emp
        CONNECT BY PRIOR empno = mgr
        START WITH job = 'PRESIDENT') e

WHERE e.deptno = d.deptno;

Note, that the SELECT list corresponds with the Inline View (Attributtes without table alias). The departement name (d.dname) does not exist within the Inline View, it is directly selected in the table DEPT using the JOIN e.deptno = d.deptno in the WHERE clause, outside the Inline View.

Chart        EmpNo Job        Dept         Boss Salary BossNo
------------ ----- ---------- ---------- ------ ------ ------
KING          7839 PRESIDENT  ACCOUNTING          5000
  JONES       7566 MANAGER    RESEARCH     KING   2975 7839
    SCOTT     7788 ANALYST    RESEARCH    JONES   3000 7566
      ADAMS   7876 CLERK      RESEARCH    SCOTT   1100 7788
    FORD      7902 ANALYST    RESEARCH     JONE   3000 7566
      SMITH   7369 CLERK      RESEARCH     FORD    800 7902
  BLAKE       7698 MANAGER    SALES        KING   2850 7839
    ALLEN     7499 SALESMAN   SALES       BLAKE   1600 7698
    WARD      7521 SALESMAN   SALES       BLAKE   1250 7698
    MARTIN    7654 SALESMAN   SALES       BLAKE   1250 7698
    TURNER    7844 SALESMAN   SALES       BLAKE   1500 7698
    JAMES     7900 CLERK      SALES       BLAKE    950 7698
  CLARK       7782 MANAGER    ACCOUNTING   KING   2450 7839
    MILLER    7934 CLERK      ACCOUNTING  CLARK   1300 7782

 Using PL/SQL to speed up UPDATEs

PL/SQL may provide an especially noticeable performance gain when you are running large batch update jobs in which parent / child updating plays a role. Consider the scenario in which the ACCOUNT (Parent) table is updated every night from the daily "collection" table BOOKING (Child). There are about 10'000 rows in ACCOUNT and approximarely 200 rows in BOOKING.

CREATE TABLE account (
acc_id      NUMBER(6)   NOT NULL,
balance     NUMBER(15)  NOT NULL,
CONSTRAINT pk_account PRIMARY KEY (acc_id));

CREATE TABLE booking (
bkg_id   NUMBER(6)   NOT NULL,
acc_id   NUMBER(6)   NOT NULL,
amount   NUMBER(15)  NOT NULL,
CONSTRAINT fk_booking_account
FOREIGN KEY (acc_id) REFERENCES account (acc_id),
CONSTRAINT pk_booking PRIMARY KEY (acc_id));

Using plain SQL may take several minutes, due the correlated subquery.

For Oracle < Version 8.1.5

UPDATE account A
SET A.balance = (SELECT B.amount + A.balance
                   FROM booking B
                  WHERE B.acc_id = A.acc_id)
WHERE EXISTS (SELECT 'X'
                FROM booking B
               WHERE B.acc_id = A.acc_id);

For Oracle >= Version 8.1.5

UPDATE account A
SET balance = balance + (SELECT amount
                           FROM booking B
                          WHERE B.acc_id = A.acc_id)
WHERE EXISTS (SELECT 'X'
                FROM booking B
               WHERE B.acc_id = A.acc_id);

Now suppose you use PL/SQL to achieve the same result. This may run in seconds.

DECLARE
  CURSOR read_amount  IS
  SELECT acc_id, amount
    FROM booking;
  --
  l_acc_id   NUMBER (6);
  l_amount   NUMBER(15);
BEGIN
  OPEN read_amount;
  LOOP
    FETCH read_amount INTO l_acc_id, l_amount;
    EXIT WHEN read_amount%NOTFOUND;
    --
    UPDATE account A
       SET balance = balance + l_amount
     WHERE acc_id  = l_acc_id;
  END LOOP;
END;

Using PL/SQL instead of traditional SQL may result in a substantial performance gains, however PL/SQL does not always produce such results. If the BOOKING table contains 1'000 or more rows, rather than 200, the result is different. If a child table updates more than 10% to 15% of the parent table, PL/SQL will actually make the update run more slowly. PL/SQL uses the table's indexes and performs more physical reads against the database than plain SQL, which performs a full table scan in this case. Always experiment with alternatives, benchmark the options, and question the results.

How to cache a table in the SGA ?

In order to cache a table in the SGA it has to be smaller than CACHE_SIZE_THRESHOLD as set in the init.ora file. However, the cost based analyzer doesn't take table cacheing into account when doing optimization so you may want to force the table using hints.

Optimize Table Structures with CAS and ORDER BY

Specify CREATE TABLE AS SELECT ORDER BY if you intend to create an index on the same key as the ORDER BY key column. Oracle will cluster data on the ORDER BY key so that it corresponds to the index key. With this "trick", the COST based Optimizer will more often use the index instead of performing a full table scan.

CREATE TABLE customer_reorg AS
SELECT FROM customer ORDER BY name;
DROP TABLE customer;
RENAME customer_reorg TO customer;
CREATE INDEX idx_cust_name ON customer(name);

Creating Oracle 7 Export Files from Oracle 8

You can create an Oracle release 7 export file from an Oracle8i database by running Oracle release 7 Export against an Oracle8i server. To do so, however, the user SYS must first run the CATEXP7.SQL script, which creates the export views that make the database look, to Export, like an Oracle release 7 database.

The following steps describe the procedure in more detail:

  1. Run the catexp7.sql script on the Oracle8i database. This script is in the $ORACLE_HOME/rdbms/admin directory.

  2. Use the Oracle7 Export utility to export the parts of the Oracle8i database containing the new or changed data.

  3. Use the Oracle7 Import utility to import the file previously exported from the Oracle8i database into the restored Oracle7 database.

How to remove in-doubt transactions ?

In doubt transactions may occur at double phase commit time for network, break node ... reason. Normally if a double phase commit failed, you may have some entries in views DBA_2PC_PENDING and DBA_2PC_NEIGHBORS. To force the in doubt transaction to rollback you have to use the command:

ROLLBACK FORCE <transaction_id>;

Unfortunately, sometime the entries are still there ... and you may discover in your alert<sid>.log file something like: ora-600 [18104] ... This point to bug 445604 Fixes in version Oracle 7.3.4. Now it's possible to use package DBMS_TRANSACTION to solve the problem if rollback force do not clean all entries.

Do as follow:

EXECUTE DBMS_TRANSACTION.PURGE_LOST_DB_ENTRY('xid');
Where 'xid' come from: SELECT local_tran_id FROM DBA_2PC_PENDING;

How to install the Help-Tables for SQLPlus and PL/SQL ?

It can be handy to have the Help-Tables for SQLPLUS online using SQL>help command. Usually, these tables in $ORACLE_HOME/sqlplus/admin/help are not installed per default, but it's easy done with the following Shell-Script.

#!/bin/sh

$ORACLE_HOME/bin/svrmgrl << EOF
  connect system/manager
  @$ORACLE_HOME/sqlplus/admin/help/helptbl.sql;
  exit;
EOF

$ORACLE_HOME/bin/svrmgrl << EOF
  connect system/manager
  @$ORACLE_HOME/sqlplus/admin/help/helpindx.sql;
  exit;
EOF

cd $ORACLE_HOME/sqlplus/admin/help

$ORACLE_HOME/bin/sqlldr userid=system/manager control=plushelp.ctl
$ORACLE_HOME/bin/sqlldr userid=system/manager control=plshelp.ctl
$ORACLE_HOME/bin/sqlldr userid=system/manager control=sqlhelp.ctl

How much Redo-Log does this Transaction generate ?

The Oracle Dicitonry is a wonderful Pool of many hidden resorces. In the Oracle System Statistic Table V$SYSSTAT you can find the Number of blocks written to the Redo. This can be found in the Attribute STATISTIC# = 71. If you measure this value before and after the transaction, you can approximately find out how much Redo-Log the transaction generates. Of course this is approximately, because there may exists other transactions at the same time.

SQL> select from v$sysstat where statistic#=71;
STATISTIC#  NAME
----------  ----------------------------------------
71          physical writes direct

Example

SQL> select value from v$sysstat where statistic#=71;
    VALUE
---------
      436

SQL> create table myhelp as select from system.help;
Table created.

SQL> select value from v$sysstat where statistic#=71;
    VALUE
---------
      642

Flush Shared Pool when it reaches 60-70% of it's capacity

On a recent project we had a problem where performance would start acceptable at the beginning of the day and by mid-day would be totally unacceptable. Investigation showed that the third party application that ran on top of the Oracle database was generating ad hoc SQL without using bind variables. This generation of ad hoc SQL and non-use of bind variables was resulting in proliferation of non-reusable code fragments in the shared pool, one user had over
90 shared pool segments assigned for queries that differed only by the selection parameter (for example "where last_name='SMITH'" instead of "where last_name='JONES'"). This proliferation of multiple nearly identical SQL statements meant that for each query issued the time to scan the shared pool for identical statements was increasing for each non-reusable statement generated.

A flush of the shared pool was the only solution to solve this performance problem, resulting that all other query returned again in less than a second.

It was determined that an automatic procedure was needed to monitor the shared pool and flush it when it reached 60-70% of capacity.

The following procedue was created:

CREATE OR REPLACE VIEW sys.sql_summary AS SELECT
   username,
   sharable_mem,
   persistent_mem,
   runtime_mem
FROM sys.v_$sqlarea a, dba_users b
WHERE a.parsing_user_id = b.user_id;

CREATE OR REPLACE PROCEDURE sys.flush_it AS

  CURSOR get_share IS
  SELECT SUM(sharable_mem)
    FROM sys.sql_summary;

  CURSOR get_var IS
  SELECT value
    FROM v$sga
   WHERE name like 'Var%';

  CURSOR get_time is
  SELECT SYSDATE
    FROM dual;

  todays_date   DATE;
  mem_ratio     NUMBER;
  share_mem     NUMBER;
  variable_mem  NUMBER;
  cur           INTEGER;
  sql_com       VARCHAR2(60);
  row_proc      NUMBER;

BEGIN

  OPEN get_share;
  OPEN get_var;

  FETCH get_share INTO share_mem;
  DBMS_OUTPUT.PUT_LINE('share_mem: '||to_char(share_mem));

  FETCH get_var INTO variable_mem;
  DBMS_OUTPUT.PUT_LINE('variable_mem: '||to_char(variable_mem));

  mem_ratio:=share_mem/variable_mem;
  DBMS_OUTPUT.PUT_LINE('mem_ratio: '||to_char(mem_ratio));

  IF (mem_ratio>0.3) THEN
    DBMS_OUTPUT.PUT_LINE ('Flushing Shared Pool ...');
    cur:=DBMS_SQL.open_cursor;
    sql_com:='ALTER SYSTEM FLUSH SHARED_POOL';
    DBMS_SQL.PARSE(cur,sql_com,dbms_sql.v7);
    row_proc:=DBMS_SQL.EXECUTE(cur);
    DBMS_SQL.CLOSE_CURSOR(cur);
  END IF;
END;
/

This procedure was then loaded into the job queue and scheduled to run every hour using the following commands:

DECLARE
  job NUMBER;
BEGIN
  DBMS_JOB.SUBMIT(job,'flush_it;',sysdate,'sysdate+1/24');
END;
/

Show who am I with my environment

set termout off
set head off
set termout on
select 'User: '|| user || ' on database ' || global_name,
       '(Terminal='||USERENV('TERMINAL')||
       ', Session-Id='||USERENV('SESSIONID')||')'
from global_name;

User: SCOTT on database ARK1.WORLD
(Terminal=ARKUM, Session-Id=150)

Check current ROLE for Database Access

When a user logs on, Oracle enables all privileges granted explicitly to the user and all privileges in the user's default roles. During the session, the user or an application can use the SET ROLE statement any number of times to change the roles currently enabled for the session. The number of roles that can be concurrently enabled is limited by the initialization parameter MAX_ENABLED_ROLES. You can see which roles are currently enabled by examining the SESSION_ROLES data dictionary view, for example:

SELECT role FROM session_roles;
ROLE
------------------------------
CONNECT
RESOURCE

You may check the DB access in your application context using the following code construct.

DECLARE
  HasAccess BOOLEAN := FALSE;
  CURSOR cur_get_role IS
  SELECT role FROM session_roles;
BEGIN
  FOR role_rec IN cur_get_role LOOP
    IF (UPPER(role_rec.role) IN ('ADMIN','CLERK')) THEN
      HasAccess := TRUE;
    END IF;
  END LOOP;
  IF (NOT HasAccess) THEN
    RAISE_APPLICATION_ERROR
    (-20020,'Sorry, you have no access to the database');
  END IF;
END;
/

Useful UNIX Utilities to manipulate fixed length records

The Unix operating system has a number of utilities that can be very useful for pre-processing data files to be loaded
with SQLLoader.  Even when the same functionality can be achieved through SQLLoader, the utilities described here will be much faster. Data warehousing applications, in particular, can benefit greatly from these utilities.

This article describes such Unix commands with examples of their utilization. The Unix version of reference here is Sun Solaris, which is based on Unix System V Release 4. For syntax details and the full range of options for each command, consult the man pages in your system and your operating system documentation.

EXAMPLE 1

Let us assume a load with the following SQLLoader control file:

LOAD DATA
INFILE 'example1.dat'
INTO TABLE emp
(empno          POSITION(01:04) INTEGER EXTERNAL,
ename           POSITION(06:14) CHAR,
job             POSITION(16:24) CHAR,
mgr             POSITION(26:29) INTEGER EXTERNAL,
sal             POSITION(31:37) DECIMAL EXTERNAL,
comm            POSITION(39:42) DECIMAL EXTERNAL,
deptno          POSITION(44:45) INTEGER EXTERNAL)

Here are the contents of data file example1.dat:

7782 CLARK     MANAGER   7839 2572.50 0.20 10
7839 KING      PRESIDENT      5850.00      10
7654 MARTIN    SALESMAN  7698 1894.00 0.15 30

EXAMPLE 2

Let us assume another load with the following control file:

LOAD DATA
INFILE 'example2.dat'
INTO TABLE dept
FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
(deptno, dname, loc)

Below are the contents of data file example2.dat:

12,RESEARCH,"SARATOGA"
10,"ACCOUNTING",CLEVELAND
13,"FINANCE","BOSTON"

The performance of direct path loads can be significantly improved by presorting the input data on indexed columns.
Pre-sorting minimizes the demand for temporary segments during the load.

The Unix command to be used for presorting is "sort".

In Example 1, suppose you have added the SORTED INDEXES (empno) clause to the control file to indicate that fields in the data file are presorted on the EMPNO column.  To do that presorting, you would enter at the Unix prompt:

sort +0 -1 example1.dat > example1.srt

This will sort file example1.dat by its first field (by default fields are delimited by spaces and tabs) and send the output to file example1.srt:

7654 MARTIN    SALESMAN  7698 1894.00 0.15 30
7782 CLARK     MANAGER   7839 2572.50 0.20 10
7839 KING      PRESIDENT      5850.00      10

In Example 2, if you wanted to sort file example2.dat by column DNAME, you would enter:

sort -t, -d +1 -2 example2.dat > example2.srt

where "-t," indicates that commas are delimiters, "-d" causes sort to consider only letters and digits in comparisons, and example2.srt is the output file:

10,"ACCOUNTING",CLEVELAND
13,"FINANCE","BOSTON"
12,RESEARCH,"SARATOGA"

Often, it is necessary to remove one or more fields from all the records in the data file.  The Unix command that does that is "cut". In Example 1, if you want to eliminate the COMM field altogether from the data file, enter at the Unix prompt:

cut -c1-38,44- example1.dat > example1.cut

where the "-c" option specifies the character ranges that you want to extract from each record.  The output file example1.cut contains:

7782 CLARK     MANAGER   7839 2572.50 10
7839 KING      PRESIDENT      5850.00 10
7654 MARTIN    SALESMAN  7698 1894.00 30

In Example 2, to eliminate the LOC field from the data file, you would enter:

cut -f1-2 -d, example2.dat > example2.cut

where "-f1-2" indicates you want to extract the first two fields of each record and "-d," tells cut to treat comma as a delimiter. The output file example2.cut would contain:

12,RESEARCH
10,"ACCOUNTING"
13,"FINANCE"

Two Unix commands can be used here: "tr" or "sed". For instance, if you want to replace all double quotes in the data file in Example 2 by single quotes, you may enter:

cat example2.dat | tr \" \' > example2.sqt

The piped "cat" is necessary because tr's input source is the standard input.  Single and double quotes are preceded by backslashes because they are special characters. The output file will be:

12,RESEARCH,'SARATOGA'
10,'ACCOUNTING',CLEVELAND
13,'FINANCE','BOSTON'

Similarly, to substitute colons for commas as delimiters in Example 2, you may enter:

sed 's/,/:/g'  example2.dat > example2.cln

The output would be:

12:RESEARCH:"SARATOGA"
10:"ACCOUNTING":CLEVELAND
13:"FINANCE":"BOSTON"

Just as for replacing characters, "tr" and "sed" can be used for eliminating them from the data file. If you want to remove all double quotes from the data file in Example 2, you may type:

cat example2.dat | tr -d \" > example2.noq

The contents of file example2.dat are piped to the tr process, in which the "-d" option stands for "delete".  The output file example2.noq would look like:

12,RESEARCH,SARATOGA
10,ACCOUNTING,CLEVELAND
13,FINANCE,BOSTON

An identical result would be obtained by using sed:

sed 's/\"//g' example2.dat > example2.noq

The string in single quotes indicates that double quotes should be replaced by an empty string globally in the input file. Another interesting usage of tr would be to squeeze multiple blanks between fields down to a single space character.   That can be achieved by doing:

cat example1.dat | tr -s ' ' ' ' > example1.sqz

The output file would look like:

7782 CLARK MANAGER 7839 2572.50 0.20 10
7839 KING PRESIDENT 5850.00 10
7654 MARTIN SALESMAN 7698 1894.00 0.15 30

Inserting characters into the data file

A typical situation in which you may need to insert characters into the datafile would be to convert a fixed position data file into a delimited one.  The data file in Example 1 is a fixed position one.  To convert it into a file delimited by commas, you would enter

cat example1.dat | tr -s ' ' ',' > example1.dlm

and obtain

7782,CLARK,MANAGER,7839,2572.50,0.20,10
7839,KING,PRESIDENT,5850.00,10
7654,MARTIN,SALESMAN,7698,1894.00,0.15,30

Merging different files into a single data file

Merging can be done by using "paste".  This command allows you to specify a list of files to be merged and the character(s) to be used as delimiter(s).  For instance, to merge the data files in Examples 1 and 2, you may enter:

paste -d' ' example1.dat example2.dat > example.mrg

where "-d' '" specifies a blank character as the delimiter between records being merged and example.mrg is the merged output file:

7782 CLARK     MANAGER   7839 2572.50 0.20 10 12,RESEARCH,"SARATOGA"
7839 KING      PRESIDENT      5850.00      10 10,"ACCOUNTING",CLEVELAND
7654 MARTIN    SALESMAN  7698 1894.00 0.15 30 13,"FINANCE","BOSTON"

The Unix command for this is "uniq".  It eliminates or reports consecutive lines that are identical.  Because only adjacent lines are compared, you may have to use the sort utility before using uniq. In Example1, suppose you wanted to keep only the first entry with DEPTNO = 10.  The Unix command would be:

uniq +43 example1.dat > example1.unq

The "+43" indicates that the first 43 characters in each record should be ignored for the comparison.  The output file example1.unq would contain:

7782 CLARK     MANAGER   7839 2572.50 0.20 10
7654 MARTIN    SALESMAN  7698 1894.00 0.15 30

Use "wc".  For example:

wc -l example1.dat
3 example1.dat

which indicates that the file contains three lines.

The "dd" Unix command can be used to convert EBCDIC data files to ASCII and vice-versa.  For example:

dd if=example1.ebc cbs=86 conv=ascii > example1.asc

takes example1.ebc as EBCDIC input file, converts it into ASCII, and writes the converted output to file example1.asc.

The "dd" and "tr" commands can also be used for converting between uppercase and lowercase characters.  Because Oracle is currently case-sensitive, this can be useful in many situations. For example, to convert all characters in file example1.dat from uppercase to lowercase, simply enter

dd if=example1.dat conv=lcase > example1.low

or

cat example1.dat | tr "[A-Z]" "[a-z]" > example1.low

The contents of output file example1.low will be:

7782 clark     manager   7839 2572.50 0.20 10
7839 king      president      5850.00      10
7654 martin    salesman  7698 1894.00 0.15 30

To convert this file back to uppercase characters, type

dd if=example1.low conv=ucase > example1.dat

or

cat example1.low | tr "[a-z]" "[A-Z]" > example1.dat

Why to use locally managed tablespaces ?

A tablespace that manages its own extents maintains a bitmap in each datafile to keep track of the free or used status of blocks in that datafile. Each bit in the bitmap corresponds to a block or a group of blocks. When an extent is allocated or freed for reuse, Oracle changes the bitmap values to show the new status of the blocks. These changes do not generate rollback information because they do not update tables in the data dictionary

Local management of extents automatically tracks adjacent free space, eliminating the need to coalesce free extents. The sizes of extents that are managed locally can be determined automatically by the system. Alternatively, all extents can have the same size in a locally-managed tablespace.

A tablespace that manages its extents locally can have either uniform extent sizes or variable extent sizes that are determined automatically by the system. When you create the tablespace, the UNIFORM or AUTOALLOCATE (system-managed) option specifies the type of allocation.

For system-managed extents, you can specify the size of the initial extent and Oracle determines the optimal size of additional extents, with a minimum extent size of 64 KB. This is the default for permanent tablespaces.

For uniform extents, you can specify an extent size or use the default size, which is 1 MB. Temporary tablespaces that manage their extents locally can only use this type of allocation.

The storage parameters NEXT, PCTINCREASE, MINEXTENTS, MAXEXTENTS, and DEFAULT
STORAGE are not valid for extents that are managed locally. Actually, you cannot create a locally managed SYSTEM tablespace. Locally managed temporary tablespaces must of type "temporary" (not "permanent").

Local management of extents avoids recursive space management operations, which can occur in dictionary-managed tablespaces if consuming or releasing space in an extent results in another operation that consumes or releases space in a rollback segment or data dictionary table. Local management of extents automatically tracks adjacent free space, eliminating the need to coalesce free extents.

Example:

  1.  An insert causes a request for an extent

  2. Oracle allocates space in the data tablespace

  3. This causes an update of system tables in the data
    dictionary if tablespace is dictionary-managed

  4. Consequently, an update is made to the redo log.

So a large number of inserts in to a tablespace with a small extent size may cause many I/O's to the system tablespace and consequently the redo log files. Also, large sorts from "read-only" databases may cause many I/O's to the log file due to system tablespace update for temporary tablespace extent allocation.

When creating tablespaces with a uniform extent size it is important to understand that 64 Kbytes per datafile is allocated for the storage management information. When creating database files, add an additional 64 Kbytes to the size of your datafile.

Consider the following example to illustrate the matter:

SQL> CREATE TABLESPACE demo1
     DATAFILE 'D:\Oradata\SAP1\tab\SAP1_demo1.dbf' SIZE 10M
     EXTENT MANAGEMENT LOCAL UNIFORM SIZE 5M;

Tablespace created.

SQL> select bytes from dba_free_space where
     TABLESPACE_NAME = 'DEMO1';

     BYTES
----------
   5242880

What happens here is we ask for 5 Mbyte extents in a 10 Mbyte file. After 64 Kbytes is allocated for the bitmap, we are left with one 5 Mbyte extent and one less then 5 Mbytes extent. We cannot use the less then 5 Mbyte extent so it does not show up -- it is wasted. This can also happen when you have larger uniform extents when the remainder of space in the datafile is just 64 Kbytes short of being able to accomodate your uniform extent size.

SQL> drop TABLESPACE demo1;

Tablespace dropped.

If you change the test case to allow for the extra 64 Kbytes:

SQL> CREATE TABLESPACE demo1
     DATAFILE 'D:\Oradata\SAP1\tab\SAP1_demo1.dbf' SIZE 10304K
     EXTENT MANAGEMENT LOCAL UNIFORM SIZE 5M;

Tablespace created.

SQL> select bytes from dba_free_space where
     TABLESPACE_NAME = 'DEMO1';

     BYTES
----------
  10485760

You can see that when we add 64 Kbytes to the datafile size the full 2 extents you want are there. Locally managed tablespaces should have datafiles that are 64 Kbytes
LARGER then a multiple of their extent size when using uniform sizing.

Download Scripts to create a database (8.1.6) with locally managed tablespaces for NT4
Download Scripts to create a database (8.1.69 with locally managed tablespaces for SUN-Solaris

How to create a locally managed temporary Tablespace ?

The syntax to create a locally managed temporary tablespace is different from the normally used syntax when creating a permanent tablespace -- find the syntax below:

### Locally managed (SIZE + 64K for Header Bitmap)
CREATE TEMPORARY TABLESPACE temp
  TEMPFILE '/u01/db/DIA2/tmp/DIA2_temp1.dbf' SIZE 512064K REUSE
  AUTOEXTEND ON NEXT 10M MAXSIZE UNLIMITED
  EXTENT MANAGEMENT LOCAL UNIFORM SIZE 256K;

You may get an ORA-03212 error message after creating locally managed tablespace. This will happen when you create an oracle user without a temporary tablespace specified; note that temporary segments cannot be created in permanent tablespaces. Due to this, always create the user with a locally managed temporary tablespace.

ORA-00604: error occurred at recursive SQL level 1
ORA-03212: Temporary Segment cannot be created in locally-managed tablespace

oerr ora 03212

03212, 00000, "Temporary Segment cannot be created in locally-managed tablespace"
// Cause: Attempt to create a temporary segment for sort/hash/lobs in
// in permanent tablespace of kind locally-managed
// Action: Alter temporary tablespace of user to a temporary tablespace
// or a dictionary-managed permanent tablespace

How to implement inheritance in a relational DB ?

Oracle8 is a object relational database, but one of the most central parts in object technology is inheritance which is not supported in many object relational databases. Therefore the big question is how inheritance can be implemented in a plain relational database. In the following example we show some possible ways. We have the generic class VEHICLE which have the three attributes A,B,C which are common to all specific classes like BIKE and CAR. In object terminology BIKE and CAR are inherited from VEHICLE. Both, BIKE and CAR may overwrite the common attributs A,B,C. Besides this, the class CAR have the attributes D,E and the class BIKE have the attrbutes F,G,H. The following figure shows the situation in object terminologie.

The shown object inheritance can be shown in an entity relationship diagram, which is used in the world of relational databases as follows:

 

 

 

 

The figure shows the Super-Entity Vehicle, with the common attributes A,B,C. These attributes are common to all entities. The entity Car and Bike are Sub-Entities, they inherit the attributes A,B,C from the Super-Entity Vehicle

The simplest solution is to create one table with all attributes. The advantage is simplicity but this solution should only be used if there are only a few attributes for CAR and VEHICLE. If you have many attributes for e.g. BIKE, most of them are NULL if you specify a car. Another disadvantage is, that all attributes D,E,F,G,H must be defined as NULL. The primary key ID in this example ID is generated with a sequence, but this is not a must.

The two table solution, one table for CAR and one table for BIKE eliminates the problem of having (many) unused attributes from the one table solution. The disadvantage is, that the common attributes A,B,C must exist in both tables. Again, the primary key is generated with the same sequence.

The three table solution eliminates all disadvantages from the above solutions, but adds some overhead. The OR constraint cannot be checked with referential integrity, therefore we need a (simple) database trigger for this.

The following code example shows solution C.

CREATE TABLE vehicle (
  ID   NUMBER(5) PRIMARY KEY,
  A    VARCHAR2(10),
  B    VARCHAR2(10),
  C    VARCHAR2(10));

CREATE TABLE car (
  ID   NUMBER(5) PRIMARY KEY,
  D    VARCHAR2(10),
  E    VARCHAR2(10));

ALTER TABLE car ADD (
  CONSTRAINT fk_car_vehicle
  FOREIGN KEY (id)
  REFERENCES vehicle (id));

CREATE TABLE bike (
  ID   NUMBER(5) PRIMARY KEY,
  F    VARCHAR2(10),
  G    VARCHAR2(10),
  H    VARCHAR2(10));

ALTER TABLE bike ADD (
  CONSTRAINT fk_bike_vehicle
  FOREIGN KEY (id)
  REFERENCES vehicle (id));

CREATE OR REPLACE TRIGGER check_or
BEFORE INSERT OR UPDATE ON bike
FOR EACH ROW
 DECLARE
   dummy CHAR(1);
   illegal_operation EXCEPTION;
   CURSOR check_or_cur (cid bike.id%TYPE) IS
    SELECT 'X' FROM car
     WHERE id = cid;
 BEGIN
   OPEN check_or_cur (:new.id);
   FETCH check_or_cur INTO dummy;
   IF check_or_cur%FOUND THEN
     RAISE illegal_operation;
   END IF;
   CLOSE check_or_cur;
 EXCEPTION
   WHEN illegal_operation THEN
     CLOSE check_or_cur;
     raise_application_error(-20000, 'ID: '|| 
     TO_CHAR(:new.id) || ' already exists');
 END;
/

INSERT INTO vehicle VALUES (1,'Has Weels','Licence','Driver');
INSERT INTO car VALUES (1,'Opel','Germany');
INSERT INTO bike VALUES (1,'Honda','Japan','2 Cyl');

ERROR at line 1:
ORA-20000: ID: 1 already exists
ORA-06512: at "SCOTT.CHECK_OR", line 17
ORA-04088: error during execution of trigger 'SCOTT.CHECK_OR'

Do NOT backup temporary tablespace

You have created a locally managed temporary tablespace and are attempting to
do a hot backup of a datafile. You issue the statement:

    SQL> ALTER TABLESPACE <TABLESPACENAME> BEGIN BACKUP;

and you receive the following error:

    ORA-03217: invalid option for alter of TEMPORARY TABLESPACE
        Cause: invalid option for alter of temporary tablespace was
               specified
       Action: Specify one of the valid options: ADD TEMPFILE

Do not back up temporary tablespaces.

This error is issued due to one of the following:

  •  Locally managed tempfiles are always set to NOLOGGING mode.

  •  Extents are managed by bitmap in each datafile to keep track
     of free or used status of blocks in that datafile.

  •  The data dictionary does not manage the tablespace.

  •  Rollback information is not generated because there is no update
     on the data dictionary.

  •  Control file does not have any reference to the tempfile.

  •  media recovery does not recognize tempfiles.

Alter database and alter tablespace will not work on tempfiles as they have no reference in the data dictionary.  There is no need to back up the tempfiles as they are used and destroyed every time you start up and shut down the database.

The locally managed tempfile is a new feature in Oracle8i to avoid recursive space management operations, which can occur in dictionary managed tablespaces.

ORA-27146: post/wait initialization failed on Solaris / Oracle 8.1.6

This message occures when oracle have a resource problem in order to start the background processes. Try to specify enough memory segments and semaphores specified in /etc/system, use the following guidelines.

SEMMNS Total semaphores available on the system as a whole
SEMMNI  Maximum number of SETs of semaphores (number of identifiers)
SEMMSL  Limits the maximum number of semaphores available in any one set
(Some platforms only).

First list out the 'processes' parameter from the "init<SID>.ora" file.

SEMMNS

Sum the number of processes in the "init<SID>.ora" file, this is the number of semaphores required by Oracle to start ALL databases. Add to this any other system requirements and ensure SEMMNS is AT LEAST this value.
SEMMNS >= SUM of 'processes' for all Databases + other system requirements.

For Oracle 8.0.x and 8.1.x allocate twice as many semaphores as are in the "init<SID>.ora" file on startup. For example, if processes = 200, Oracle will need 400 to startup the SGA. This 
needs to be part of your calculations.
Example for Oracle 8.1.6: 
If you have 3 databases and the "init.ora" files have 100  150 and 200 processes allocated for each database then you would add up the three numbers 100+150+200 = 450 and an extra 10 processes per database 450+30 = 480. You would need to set SEMMNS to at least twice this number (480 2 = 960 SEMMNS=960).

SEMMNI

Semaphores are allocated by Unix in 'sets' of up to SEMMSL semaphores per set. You can have a MAXIMUM of SEMMNI sets on the system at any one time. SEMMNI is an arbitrary figure which is best set to a round figure no smaller that the smallest 'processes' figure for any database on the system, in our example we would set SEMMNI=100 (see above).

SEMMSL

We usually set SEMMSL to the same value as SEMMNI.

Reboot the Solaris Machine after editing /etc/system. Do an ipcs -s to find out what semaphores are hold by oracle. If no oracle processes are running then no semaphores should be hold by the owner oracle. To remove the semaphores do an iprm -s ID where ID the semaphore identifier.


Kernel Parameters for Oracle 8.1.6 (Example for three DB's)
set shmsys:shminfo_shmmax=4294967295
set shmsys:shminfo_shmmin=1
set shmsys:shminfo_shmmni=100
set shmsys:shminfo_shmseg=10
set semsys:seminfo_semmni=100
set semsys:seminfo_semmsl=100
set semsys:seminfo_semmns=1000
set semsys:seminfo_semopm=100

Create a CROSS MATRIX report using DECODE

Example of a CROSS MATRIX report implemented using standard SQL.

SELECT job,
       sum(decode(deptno,10,sal)) "Dept10",
       sum(decode(deptno,20,sal)) "Dept20",
       sum(decode(deptno,30,sal)) "Dept30",
       sum(decode(deptno,40,sal)) "Dept40"
 FROM scott.emp
GROUP BY job
/

JOB          Dept10    Dept20    Dept30    Dept40
--------- --------- --------- --------- ---------
ANALYST                  6000
CLERK          1300      1900       950
MANAGER        2450      2975      2850
PRESIDENT      5000
SALESMAN                           5600

Storage of Oracle Data Types

Oracle supports different data types which allows the database designer to define the length or precision of these types. Specially VARCHAR2 and NUMBER are scalable.

One of the main advantage of the data type VARCHAR2 is the variable length. As most database designers know, only the used number of characters up to the defined length will be stored in the database. No spaces are padded up to the specified size for VARCHAR2.
This behaviour can be checked easily: Two tables are defined, one with a small and another with a larger number of bytes.

CREATE TABLE shortVar2 (shorttext VARCHAR2(12));
CREATE TABLE longVar2  (longtext VARCHAR2(2000));

Now some records are inserted in both tables. The length of the inserted text is equivalent, in this example 11 characters:

FOR i IN 1..25000 LOOP
  INSERT INTO shortVar2 VALUES ('Hello world');
  INSERT INTO longVar2 VALUES ('Hello world');
END LOOP;

Both tables can be analysed and the result is not surprising:

TABLE_NAME                      NUM_ROWS    BLOCKS AVG_ROW_LEN
------------------------------ --------- --------- -----------
LONGVAR2                           25000       120          15
SHORTVAR2                          25000       120          15

In both tables 120 blocks are used and the average row length is 15 bytes, regardless of the specified maximum row size. Some overhead bytes are used to determine the length of the stored number of bytes and for row information.

The analyse for VARCHAR2 was not surprising. But how does Oracle stores numbers? Does NUMBER(2) need less, equal, or more storage than NUMBER(15) or even NUMBER? Let's do the same steps as above to analyse the result: Three tables are defined, one for NUMBER(2) only, one for the maximum precision but filled with the same value as the first table, and one for the maximum precision filled with very big numbers.

CREATE TABLE num2num2 (num2 NUMBER(2));
CREATE TABLE numXnum2 (numX NUMBER);
CREATE TABLE numXnumX (numX NUMBER);

Again some records are inserted in every table:

FOR i IN 1..25000 LOOP
  INSERT INTO num2num2 VALUES (25);
  INSERT INTO numXnum2 VALUES (25);
  INSERT INTO numXnumX VALUES
  (99999999123456789012345678901234567890);
END LOOP;

The result of the analyse:

TABLE_NAME                      NUM_ROWS    BLOCKS AVG_ROW_LEN
------------------------------ --------- --------- -----------
NUM2NUM2                           25000        80           6
NUMXNUM2                           25000        80           6
NUMXNUMX                           25000       182          24

Both tables num2num2 and numXnum2 (filled with the same value) are using 80 blocks and have an average record length of 6 bytes. Only the storage of very big numbers needs more blocks and increases the average record length up to 24 bytes. Some overhead bytes are used to determine the length (one byte) and for row information.

Positive numbers are stored in the following format:

<Sign (1 bit), exponent based on 64 (7 bit)><number based on 100><number base on 100><number based on 100>...

E.g. the number 345 will be split to <3><45> and stored within three bytes as follows:

<194><4><46>

  • 194 (decimal) has the bit pattern 1100 0010. The first bit represents the sign (positive number), the next 7 bits represent the exponent (64 plus 2). This will be interpreted as 100 to the power of 2 (equal to 10000).
     

  • 4 is the sum of 3 plus 1 because Oracle always adds 1 to the original splitted
    number to avoid zero.
     

  • 46 is the sum of 45 plus 1.

So the value will be calculated for this positive number as 0.345 multiplied by 10000.

Negative numbers are stored and calculated in a similar way.

Oracle has an efficient way to store strings and numbers with variable length. There is no reason to shorten the length. No disk space is wasted because Oracle takes as much space as really needed.

Thanks to Oracle Software (Schweiz) for this information.



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