oracle delete temporary table

Oracle is a powerful relational database management system. In the process of using Oracle, we often need to create temporary tables to temporarily store some data or perform some temporary data processing operations. However, after the temporary table is used, we also need to delete it to release database resources. So, in this article, I will introduce how to delete temporary tables in Oracle.

1. What is a temporary table?

A temporary table is a special Oracle table used to temporarily store and process data during a user session. They can store query results, return values from stored procedures, or store other data. Temporary tables are limited and will be automatically deleted when the session ends.

2. How to create a temporary table?

In Oracle, we can use the CREATE GLOBAL TEMPORARY TABLE statement to create a temporary table. For example, the following statement will create a temporary table named temp_table:

CREATE GLOBAL TEMPORARY TABLE temp_table (
id NUMBER,
name VARCHAR2(20));

In this example, we create a temporary table temp_table containing two columns: id and name.

3. How to delete the temporary table?

1. Ordinary deletion

The statement to delete a table in Oracle is DROP TABLE. Ordinary tables can be deleted using the DROP TABLE statement, but the deletion method of temporary tables is slightly different from that of ordinary tables. We cannot directly delete the temporary table using the ordinary DROP TABLE statement, because the temporary table only exists in the current session.

If we use the DROP TABLE statement to delete the temporary table, an error message will appear: ORA-00942: table or view does not exist. This is because Oracle will not be able to find the table because it has been destroyed.

Therefore, in Oracle, we need to use the TRUNCATE TABLE statement or close the temporary table in the current session to delete the temporary table. These two methods will be introduced separately below.

2.TRUNCATE TABLE deletion

One way to delete a temporary table is to use the TRUNCATE TABLE statement. The TRUNCATE TABLE statement is very similar to the DROP TABLE statement and both can delete tables from the Oracle database. But there are some important differences between them.

The DROP TABLE statement will delete the table in the Oracle database and completely delete the table and its related objects. The TRUNCATE TABLE statement only deletes all rows in the table, but does not delete the table itself. When we use the TRUNCATE TABLE statement, Oracle will automatically release the table's storage space. Therefore, the TRUNCATE TABLE statement is faster and more resource-efficient than the DROP TABLE statement.

The following is an example of using the TRUNCATE TABLE statement to delete a temporary table:

TRUNCATE TABLE temp_table;

When using the TRUNCATE TABLE statement, it should be noted that this statement can only All data in the temporary table is deleted, but the definition of the temporary table remains. The advantage of this is that after the session ends, the temporary table can be used again without having to redefine it.

3. Close session deletion

In Oracle, temporary tables only exist in the current session. Therefore, closing the current session can directly delete a temporary table. There are two ways to close a session: one is to use the exit statement, the other is to use the following statement to close the current session:

ALTER SESSION CLOSE DATABASE LINK ...

In this statement, We just need to replace... with the database link name of the current session connection. After executing this statement, Oracle will close the current session and all temporary tables created during the session will be automatically deleted.

4. Summary

In Oracle, a temporary table is a special table type used to temporarily store data and perform data processing. When using temporary tables, we need to pay attention to deletion operations to avoid occupying Oracle database resources. In this article, we introduced three methods to delete Oracle temporary tables: TRUNCATE TABLE statement, close the current session and DROP TABLE statement. No matter which method is used, it needs to be operated with caution to avoid unnecessary losses.

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