Question

我有一个一对多的表，其中包含这些用户的ID和特征。我想将一个用户的设置复制到另一个用户。

userid    trait    onoff
------    -----    -----
1          1         on
1          2         on
1          3         on
1          4         on
2          1         off
2          2         off
2          3         off
2          4         off

所以我想将用户1的onoff值复制到2，以便user2在完成后将所有内容都打开。

更新表设置onoff =（从userid = 1的表中选择onoff）userid = 2

这是基本的想法，但显然不起作用。我想我希望服务器根据相关子查询进行思考，但外部部分不是查询，而是更新。

这是否可以一步到位？

Answer 1

试试这个，userid = 2将获得useid = 1值：

UPDATE u2
    SET onoff=u1.onoff
    FROM YourTable  u2
        INNER JOIN YourTable u1 ON u2.trait=u1.trait    
    WHERE u2.userid=2 AND u1.userid=1

完整的SQL Server 2005+示例：

DECLARE @YourTable table (userid int,trait int, onoff varchar(3))
INSERT INTO @YourTable VALUES (1,          1,         'on')
INSERT INTO @YourTable VALUES (1,          2,         'on')
INSERT INTO @YourTable VALUES (1,          3,         'on')
INSERT INTO @YourTable VALUES (1,          4,         'on')
INSERT INTO @YourTable VALUES (2,          1,         'off')
INSERT INTO @YourTable VALUES (2,          2,         'off')
INSERT INTO @YourTable VALUES (2,          3,         'off')
INSERT INTO @YourTable VALUES (2,          4,         'off')

select * from @YourTable order by userid,trait

UPDATE u2
    SET onoff=u1.onoff
    FROM @YourTable  u2
        INNER JOIN @YourTable u1 ON u2.trait=u1.trait    
    WHERE u2.userid=2 AND u1.userid=1

select * from @YourTable order by userid,trait

输出

userid      trait       onoff
----------- ----------- -----
1           1           on
1           2           on
1           3           on
1           4           on
2           1           off
2           2           off
2           3           off
2           4           off

(8 row(s) affected)

(4 row(s) affected)

userid      trait       onoff
----------- ----------- -----
1           1           on
1           2           on
1           3           on
1           4           on
2           1           on
2           2           on
2           3           on
2           4           on

(8 row(s) affected)

Answer 2

MERGE在SQL-99标准中引入，在SQL：2003中进行了改进，并由多个供应商实现（和扩展）（例如SQL Server 2008，Oracle，postgreSQL）：

MERGE INTO YourTable
   USING (
          SELECT userid, trait, onoff
            FROM YourTable
           WHERE userid = 2
         ) AS S
      ON YourTable.userid = 1
         AND S.trait = YourTable.trait
WHEN MATCHED THEN 
   UPDATE
      SET onoff = S.onoff
WHEN NOT MATCHED THEN
   INSERT (userid, trait, onoff)
      VALUES (userid, trait, onoff);

我可以使用SQL来更新来自另一个表的多个值的多个行吗？

2 个答案: