oracle temporary table deletion

Detailed explanation of Oracle temporary table deletion method

In Oracle database, a temporary table is a temporary table that is usually used to store temporary data, such as intermediate result sets, etc. Since temporary tables only exist for a certain life cycle in the database, they often need to be deleted. This article will introduce in detail the deletion method of temporary tables in Oracle database.

1. Use the DROP TABLE command to delete a temporary table

The DROP TABLE command is a common command to delete a table in Oracle database. This command can also be used when deleting a temporary table. The syntax is as follows:

DROP TABLE table_name [CASCADE CONSTRAINTS];

Among them, table_name represents the name of the temporary table to be deleted. CASCADE CONSTRAINTS is an optional parameter. When this parameter is used, it means that the foreign key constraints on the table will be deleted when the table is deleted.

2. Use the TRUNCATE TABLE command to delete a temporary table

The TRUNCATE TABLE command is also one of the common commands to delete a table in the Oracle database. It is mainly used to quickly delete data in the table. , while preserving the structure of the table. The TRUNCATE TABLE command is also an optional method when dropping a temporary table. The syntax is as follows:

TRUNCATE TABLE table_name;

Among them, table_name represents the name of the temporary table to be deleted.

It should be noted that using the TRUNCATE TABLE command will clear all data in the table and will not trigger triggers on the table.

3. Use the DROP GLOBAL TEMPORARY TABLE command to delete a temporary table

The DROP GLOBAL TEMPORARY TABLE command is a command specifically used to delete temporary tables in the Oracle database. Its syntax is as follows:

DROP GLOBAL TEMPORARY TABLE table_name;

Among them, table_name represents the name of the temporary table to be deleted. It should be noted that using the DROP GLOBAL TEMPORARY TABLE command will delete the global temporary table.

4. Use the IF EXISTS clause to determine whether the temporary table exists

When deleting the temporary table, make sure that the table to be deleted actually exists, otherwise an error will occur. To avoid this situation, you can use the IF EXISTS clause to determine whether the table exists. The syntax is as follows:

DROP TABLE IF EXISTS table_name [CASCADE CONSTRAINTS];

Among them, table_name represents the name of the temporary table to be deleted, and CASCADE CONSTRAINTS is an optional parameter, indicating that the foreign key constraints on the table will be deleted at the same time when the table is deleted. If the table name does not exist, the DROP TABLE statement will not execute.

5. Use system views V$SESSION and V$SORT_USAGE to query temporary tables

In actual applications, sometimes it is necessary to query the temporary table being used to confirm whether Delete the table. Oracle database provides two system views V$SESSION and V$SORT_USAGE. By querying these two views, you can easily obtain the temporary table information currently in use.

The V$SESSION view contains information about all current sessions in the Oracle database. You can find the temporary table in use by querying the view for the session SID and SERIAL#. The SQL to query this view is as follows:

SELECT s.sid, s.serial# 
FROM v$session s, v$sort_usage su 
WHERE s.saddr = su.session_addr 
AND su.tablespace_name = '临时表空间名称' 
AND su.operation = 'Sort';

It should be noted that the temporary table must be stored in the temporary table space. You can modify the "temporary table space name" in SQL to the actual space name according to your own needs.

V$SORT_USAGE view can display all sorting operation information currently in use, and you can use this view to find the temporary table in use. The SQL to query this view is as follows:

SELECT s.sid, s.serial#, su.tablespace_name, su.segment_name 
FROM v$session s, v$sort_usage su 
WHERE s.saddr = su.session_addr 
AND su.tablespace_name = '临时表空间名称' 
AND su.operation = 'Sort';

By querying the above two system views, the temporary table being used can be easily located for deletion operations.

Summary: Temporary tables are a commonly used temporary storage method in Oracle databases, and their deletion methods are also relatively diverse. This article introduces the various methods available in the database to delete temporary tables, and provides an example of using system views to query information about temporary tables in use. Mastering these methods can help database administrators better manage temporary tables to improve database performance and operating efficiency.

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