Temporary tables

Informix^® temporary tables are created through the CREATE TEMP TABLE DDL instruction or through a SELECT ... INTO TEMP statement. Temporary tables are automatically dropped when the SQL session ends, but they can also be dropped with the DROP TABLE command. There is no name conflict when several users create temporary tables with the same name.

Informix allows you to create indexes on temporary tables. No name conflict occurs when several users create an index on a temporary table by using the same index identifier.

Note: BDL reports create a temporary table when the rows are not sorted externally (by the source SQL statement).

IBM^® DB2^® 7 supports the DECLARE GLOBAL TEMPORARY TABLE instruction. Native DB2 temporary tables are quite similar to Informix temporary tables with some exceptions:

A 'user temporary table space' must exist for the database.
Users must have 'USE' privilege on a 'user temporary table space'.
For usage, the temporary table name must be prefixed by 'SESSION'.
No constraints or indexes can be created on temporary tables.

For more details, see the DB2 documentation.

Solution

In accordance with some prerequisites, temporary tables creation in BDL programs can be supported by the database interface.

How does it work ?

Informix-specific statements involving temporary table creation are automatically converted to IBM DB2 "DECLARE GLOBAL TEMPORARY TABLE" statements.
Once the temporary table has been created, all other SQL statements performed in the current SQL session are parsed to add the SESSION prefix to the table name automatically.

Prerequisites

Fulfill the DB2 prerequisites to create global temporary tables, at minimum you must create a user temporary table space and grant the usage to database users:
```
CREATE USER TEMPORARY TABLESPACE tempspace01 MANAGED BY AUTOMATIC STORAGE
GRANT USE OF TABLESPACE tempspace01 TO PUBLIC
```
See DB2 documentation for more details.

Limitations

Tokens matching the original table names are converted to unique names in all SQL statements. Make sure you are not using a temp table name for other database objects, like columns. The following example illustrates this limitation:
```
CREATE TEMP TABLE tmp1 ( col1 INTEGER, col2 CHAR(20) )
SELECT tmp1 FROM table_x WHERE ... 
```
Only the 'native' serial emulation mode is supported with temporary tables. See the issue about SERIALs for more details.