How to query temporary table in oracle

Oracle is a widely used database management system that provides a rich query language and tools that allow users to easily query data in the database. In database application development, temporary tables are a very useful method. They can be used to temporarily store query results or intermediate data for further processing. In this article, we will explain how to query temporary tables in Oracle.

What is a temporary table

In Oracle, a temporary table is a special table that is created in memory or disk to store temporary data or intermediate results. Temporary tables typically exist only during query or procedure execution, and are automatically deleted when they are no longer needed. Temporary tables can contain the same columns and constraints as regular tables, and they can also be used in queries.

To create and use temporary tables in Oracle, you can use the CREATE GLOBAL TEMPORARY TABLE or CREATE PRIVATE TEMPORARY TABLE statement. The CREATE GLOBAL TEMPORARY TABLE statement is used to create a global temporary table, which is defined at the system level and can be accessed by multiple sessions simultaneously. The CREATE PRIVATE TEMPORARY TABLE statement is used to create a private temporary table that can only be used by the session that created it.

How to query a temporary table

In Oracle, querying a temporary table is the same as querying a normal table, but requires the use of specific syntax. When querying a temporary table, you need to first determine whether the temporary table exists. If the temporary table already exists, it can be queried using the SELECT statement. The following is a simple example of querying a temporary table:

SELECT * FROM table_name;

where table_name is the name of the temporary table to be queried. Before executing this query, you need to ensure that the temporary table has been created.

If you want to query the temporary table in the current session, you can use the following statement:

SELECT * FROM SESSION.table_name;

where SESSION is the name of the current session.

When querying a temporary table, you can also use the WHERE clause to filter. For example, if you want to query the rows whose age column is greater than 20 in a global temporary table named tmp_table, you can use the following statement:

SELECT * FROM tmp_table WHERE age > 20;

If you want To query a private temporary table, you need to create it using the CREATE PRIVATE TEMPORARY TABLE statement before querying it. The syntax for querying a private temporary table is the same as querying a global temporary table.

Notes

When querying the temporary table, you need to pay attention to the following points:

1. Ensure that the temporary table has been created: Before querying the temporary table, you need to ensure that the temporary table The table has been created and is available in the current session.

2. Pay attention to the table name: When querying the temporary table, you need to use the correct table name.

3. Pay attention to column names and types: In the SELECT statement, you need to ensure that the column names and types match the definition of the temporary table.

4. Pay attention to the WHERE clause: When using the WHERE clause, you need to ensure that the conditions comply with the data type and range in the temporary table.

Summary

Temporary tables are a very useful database technology and are widely used in Oracle. The syntax for querying temporary tables is similar to querying ordinary tables, but you need to pay attention to some special query methods and precautions. Knowing how to query temporary tables is very important for developers and administrators working with Oracle databases.

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