如何使用DB2限制DELETE中的行数？

Question

当我在DB2表上删除带有SQL请求的行时,我想在敏感表上添加安全性.

我想模仿MySQL允许您限制SQL请求中删除的行数的方式.

基本上我想用DB2做这个:

DELETE FROM table WHERE info = '1' LIMIT 1

有没有办法用DB2做到这一点？

Answer 1

delete from table where id in (select id from table where info = '1' order by id fetch first 1 rows only)

Answer 2

这真的取决于你的平台.

如果您在Linux/Unix/Windows上使用DB2,则可以创建一个获取所需行的select,并将其作为删除子查询,DB2将能够删除select的结果.像这样:

DELETE FROM (
    SELECT 1
    FROM table
    WHERE info = '1'
    ORDER BY your_key_columns
    FETCH FIRST ROW ONLY
) AS A
;

如果您使用的是DB2 for z/OS,那么该语法不起作用.但是,你可以使用你的主键基本上做同样的事情(这个也适用于LUW):

DELETE FROM table
WHERE (info, key2) IN (
    SELECT info, key2
    FROM table
    WHERE info = 1
    ORDER BY key2
    FETCH FIRST ROW ONLY
);

这是一个示例脚本,演示了如何使用它:

DECLARE GLOBAL TEMPORARY TABLE SESSION.TEST(
     ID INT
    ,RN INT
) ON COMMIT PRESERVE ROWS;

INSERT INTO SESSION.TEST 
    SELECT 1,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 1,2 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 1,3 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 1,4 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 1,5 FROM SYSIBM.SYSDUMMY1 UNION ALL

    SELECT 2,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 2,2 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 2,3 FROM SYSIBM.SYSDUMMY1 UNION ALL

    SELECT 3,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 3,2 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 3,3 FROM SYSIBM.SYSDUMMY1 UNION ALL

    SELECT 4,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 4,2 FROM SYSIBM.SYSDUMMY1 UNION ALL

    SELECT 5,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 6,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 7,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 8,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 9,1 FROM SYSIBM.SYSDUMMY1 UNION ALL
    SELECT 10,1 FROM SYSIBM.SYSDUMMY1
;

SELECT * FROM SESSION.TEST ORDER BY ID, RN;

-- LUW Version
DELETE FROM (
    SELECT 1
    FROM SESSION.TEST
    WHERE ID = 1
    ORDER BY RN
    FETCH FIRST ROW ONLY
) AS A
;

--Mainframe version
DELETE FROM SESSION.TEST
WHERE (ID, RN) IN (
    SELECT ID, RN
    FROM SESSION.TEST
    WHERE ID = 1
    ORDER BY RN
    FETCH FIRST ROW ONLY
);

SELECT * FROM SESSION.TEST ORDER BY ID, RN;

DROP TABLE SESSION.TEST;