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Global Temporary Table

Create Temporary Table in Oracle

To create a table named test with column col1 type varchar2 length 10, col2 type number. col3 type clob we can use CREATE TABLE statement as,
CREATE TABLE TEST(col1 VARCHAR2(10), col2 NUMBER, col3 CLOB);
Now if I insert data into the table the data is visible and accessible to all users. In many cases it is needed the data inside a table will be reside temporarily. In that case we can use temporary tables. Temporary tables are useful in applications where a result set is to be buffered. To create temporary table we have to issue CREATE GLOBAL TEMPORARY clause.
Temporary table can be of two types based on ON COMMIT clause settings.
1)ON COMMIT DELETE ROWS specifies temporary table would be transaction specific. Data persist within table up to transaction ending time. If you end the transaction the database truncates the table (delete all rows). Suppose if you issue commit or run ddl then data inside the temporary table will be lost. It is by default option.
Example:
(i)This statement creates a temporary table that is transaction specific:
CREATE GLOBAL TEMPORARY TABLE test_temp(col1 number, col2 number) ON COMMIT DELETE ROWS;
Table created.
(ii)Insert row in to the temporary table.
insert into test_temp values(3,7);
1 row created.
(iii)Look at the data in the table.
select * from test_temp;
COL1 COL2
———- ———-
3 7
(iv)Issue Commit.
commit;
Commit complete.
(v)Now look at the data in the temporary table. As I created transaction specific temporary table(on commit delete rows) so data is lost after commit.
SQL> select * from test_temp;
no rows selected
2)ON COMMIT PRESERVE ROWS specifies temporary table would be session specific. Data persist within table up to session ending time. If you end the session the database truncates the table (delete all rows). Suppose you type exit in SQL*Plus then data inside the temporary table will be lost.
Example of Session Specific Temporary Tables:
1)Create Session Specific Temporary Table test_temp2.
CREATE GLOBAL TEMPORARY TABLE test_temp2 (col1 number, col2 number)
ON COMMIT PRESERVE ROWS;
(ii)Insert data into it and look at data both before commit and after commit.
insert into test_temp2 values(3,7);
1 row created.
SQL>select * from test_temp2;
COL1 COL2
———- ———-
3 7
(iii) commit;
Commit Complete
(iv)select * from test_temp2;
COL1 COL2
———- ———-
3 7

(iv)End the Session.
exit;


Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 – Production
With the Partitioning, OLAP and Data Mining options
(v)Connect in a new session and look at data again.
$ sqlplus apps/apps@vis.world
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 – Production
With the Partitioning, OLAP and Data Mining options

SQL> select * from test_temp2;
no rows selected

This is how Global Temporary Tables are used.
Feature of Temporary Table
1.Indexes can be created on temporary tables. They are also temporary and the data in the index has the same session or transaction scope as the data in the underlying table.
2.Unlike permanent tables, temporary tables and their indexes do not automatically allocate a segment when they are created. Instead, segments are allocated when the first INSERT (or CREATE TABLE AS SELECT) is performed. This means that if a SELECT, UPDATE, or DELETE is performed before the first INSERT, the table appears to be empty.
3.DDL operations (except TRUNCATE) are allowed on an existing temporary table only if no session is currently bound to that temporary table.
4.If you rollback a transaction, the data you entered is lost, although the table definition persists.
5.A transaction-specific temporary table allows only one transaction at a time. If there are several autonomous transactions in a single transaction scope, each autonomous transaction can use the table only as soon as the previous one commits.
6.Because the data in a temporary table is, by definition, temporary, backup and recovery of temporary table data is not available in the event of a system failure.
7.It is good to know about that temporary table itself is not temporary, the data within it is temporary.
Restriction of Temporary Table
1.Temporary tables cannot be partitioned, clustered, or index organized.
2.You cannot specify any foreign key constraints on temporary tables.
3.Temporary tables cannot contain columns of nested table.
4.You cannot specify the following clauses of the LOB_storage_clause: TABLESPACE, storage_clause, or logging_clause.
5.Parallel DML and parallel queries are not supported for temporary tables. Parallel hints are ignored. Specification of the parallel_clause returns an error.
6.You cannot specify the segment_attributes_clause, nested_table_col_properties, or parallel_clause.
7.Distributed transactions are not supported for temporary tables.

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