sql - 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 做到这一点：

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，您只需创建一个获取所需行的选择，并将其作为删除的子查询，DB2 将能够删除您选择的结果。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，那么不幸的是，该语法不起作用。但是，您可以使用您的主键来做基本相同的事情（这也适用于 LUW）：

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

---

这是一个演示如何使用它的示例脚本：

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;

Answer 3

如果您的主键有多个值，或者您只需要多个值作为条件，则此查询有效：

DELETE FROM TABLE
WHERE (COLUMN1, COLUMN2) IN (
    SELECT COLUMN1, COLUMN2 FROM TABLE
    WHERE SOME_COLUMN='THIS'
    AND SOME_OTHER_COLUMN LIKE 'THAT%'
    FETCH FIRST 10 ROWS ONLY)

Answer 4

在 IBMi DB2 上：

DELETE FROM table WHERE RRN(table) in 
(SELECT RRN(table) FROM table WHERE col1 = '1' AND col2 = '2' FETCH FIRST 5 ROWS ONLY)

Answer 5

这个查询怎么样？

delete from table D where exists 
 ( select * from ( select * from table M fetch first 10 rows only ) as M
   where M.object_id = D.object_id )

Answer 6

MERGE INTO XYZ A<BR>
USING (<BR>
SELECT RID_BIT(B) CHAVE<BR>
FROM XYZ B<BR>
FETCH FIRST 100000 ROWS ONLY) B<BR>
ON RID_BIT(A) = B.CHAVE<BR>
WHEN MATCHED THEN DELETE;

Answer 7

只需选择一个语句，并将该语句放在删除查询中：

delete from (
select from table WHERE info = '1' order by id fetch first 25000 rows only
)

Answer 8

DELETE                                      
FROM Bibl/File                             
WHERE RRN(File) =  (                        
                    SELECT min(RRN(File))   
                    FROM Bibl/File         
                    WHERE Fld1 = 'xx'     
                   )   

RRN 功能仅适用于 AS400/iSeries/PowerSystem。在其他环境中，相对记录号还有其他功能。

这使得即使没有 UNIQUE 键也可以擦除多个相同的记录。它也可用于通过细微更改进行更新。

像 LIMIT 一样工作，但使用 DELETE 和/或 UPDATE。

它仅适用于 SQL DB2 其他设置应由 RRN 函数更改以返回列号

Answer 9

DELETE FROM table
WHERE info = '1'
FETCH FIRST 1 ROWS ONLY