How to create temporary table in oracle stored procedure

Oracle stored procedures are a programming method in Oracle database that allow users to write code and store it in the database so that it can be used repeatedly when needed. Stored procedures can execute a set of SQL statements or other program code, and can accept input parameters and return output results.

In Oracle stored procedures, temporary tables are a very practical function, which can be used to store temporary data sets for subsequent processing. This article will delve into the implementation of temporary tables in Oracle stored procedures.

1. Introduction to temporary tables in Oracle stored procedures

In Oracle, a temporary table is an object similar to a normal table, but it only exists in the current session and will be terminated when the session ends. will be automatically deleted. Temporary table is a temporary storage structure provided by Oracle database, which can conveniently store some temporarily generated data for subsequent processing. Unlike ordinary tables, the data of temporary tables will not be persisted to disk.

Oracle supports two types of temporary tables: global temporary tables and local temporary tables. A global temporary table is a temporary table that can be shared by multiple sessions, while a local temporary table can only be accessed by the session that created it. Since global temporary tables exist in the database, they are more practical than local temporary tables in some scenarios.

In the storage process, temporary tables can be used to store intermediate result sets to reduce the number of data reads and writes and speed up processing. In a complex stored procedure, the intermediate result set may need to be processed multiple times. In order to avoid frequent access to the database, it is a good choice to store the intermediate result set in a temporary table.

2. How to create temporary tables in Oracle stored procedures

The way to create temporary tables in Oracle stored procedures is similar to creating ordinary tables. Just add "##" or " #" can be used as a prefix. Among them, "##" means creating a global temporary table, and "#" means creating a local temporary table.

For example, the following code demonstrates how to create a global temporary table:

CREATE GLOBAL TEMPORARY TABLE ##TEMP_TABLE
(
    ID NUMBER(10),
    NAME VARCHAR2(100)
) ON COMMIT PRESERVE ROWS;

In the above code, "ON COMMIT PRESERVE ROWS" means to retain all row data in the table when the transaction is committed. , instead of clearing the data in the table.

The following is an example of creating a local temporary table:

CREATE GLOBAL TEMPORARY TABLE #TEMP_TABLE
(
    ID NUMBER(10),
    NAME VARCHAR2(100)
) ON COMMIT PRESERVE ROWS;

Of course, you can also add indexes, constraints, etc. to the definition of the table to meet actual needs.

3. Using temporary tables in Oracle stored procedures

In Oracle stored procedures, you need to pay attention to the following points when using temporary tables:

1. In stored procedures Before using a temporary table, you need to create the table first, which can be done at the beginning of the stored procedure.
2. After the execution of the stored procedure is completed, the data in the temporary table needs to be cleared, which can be achieved using the DELETE statement.
3. When the stored procedure ends, the global temporary table will be automatically deleted, and the local temporary table needs to be deleted through the DROP TABLE statement.

The following example demonstrates the use of temporary tables in Oracle stored procedures:

CREATE OR REPLACE PROCEDURE PROCESS_DATA AS
BEGIN
    -- 创建全局临时表
    CREATE GLOBAL TEMPORARY TABLE ##TEMP_TABLE
    (
        ID NUMBER(10),
        NAME VARCHAR2(100)
    ) ON COMMIT PRESERVE ROWS;
    
    -- 插入数据到临时表中
    INSERT INTO ##TEMP_TABLE(ID, NAME) VALUES (1, '张三');
    INSERT INTO ##TEMP_TABLE(ID, NAME) VALUES (2, '李四');
    INSERT INTO ##TEMP_TABLE(ID, NAME) VALUES (3, '王五');
    
    -- 处理临时表中的数据
    FOR item IN (SELECT * FROM ##TEMP_TABLE)
    LOOP
        DBMS_OUTPUT.PUT_LINE(item.ID || ' ' || item.NAME);
    END LOOP;
    
    -- 清除临时表中的数据
    DELETE FROM ##TEMP_TABLE;

    -- 删除全局临时表
    DROP TABLE ##TEMP_TABLE;
END;

In the above example, a global temporary table ##TEMP_TABLE is first created and inserted got some data. Then the data in the temporary table is processed, the contents in the temporary table are cleared, and finally the temporary table is deleted.

Summary:

In Oracle stored procedures, temporary tables are a convenient and efficient way to process data. By using temporary tables, you can avoid frequent access to the database and improve the execution speed of stored procedures. When using a temporary table, you need to pay attention to clearing the data in the table and manually delete the table when necessary to avoid some unexpected exceptions.

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