使用aggregate函数返回的值进行更新

Question

如何使用sql update语句中的聚合函数更新表的列？

Answer 1

根据定义,聚合函数将输入的一个或多个记录聚合到结果集中的单个记录中,因此您想要更新哪个记录并不明显.

通常,您可以在子查询中使用聚合函数:

UPDATE  mytable
SET     mycol = 
        (
        SELECT  SUM(othercol)
        FROM    othertable o
        WHERE   o.yetothercol = m.yetmycol
        )

,在JOIN(工作MySQL和SQL Server)

UPDATE  mytable
JOIN    (
        SELECT  yetothercol, SUM(othercol) AS psum
        FROM    othertable
        GROUP BY
                yetothercol
        ) s
ON      yetmycol = yetothercol
SET     mycol = psum

,或在MERGE声明中(在Oracle和中工作SQL Server 2008):

MERGE
INTO    mycol
USING   (
        SELECT  yetothercol, SUM(othercol) AS psum
        FROM    othertable
        GROUP BY
                yetothercol
        ) s
ON      (yetmycol = yetothercol)
WHEN MATCHED THEN
UPDATE
SET     mycol = psum