sql 一个多表连接的更新语句

update A,B,C set A.ls=C.ls where A.bmid=B.bmid and B.dj=C.dj

或者：

update A as a,B as b,C as c set a.ls=c.ls where a.bmid=b.bmid and b.dj=c.dj

update A set A. nature='XXX' from A, B, C where A.id=B.rowid and B.rowid=C.kid and (这里写你的条件， 比如什么哪个表的ID)

可以这样更新

update Product SET 库存= T1.数量 - T2.数量

from

(select 商品名称,sum(数量) as 数量 from purchase group by 商品名称) as T1,

(select 商品名称,sum(数量) as 数量 from sale group by 商品名称) as T2

where T1.商品名称 = T2.商品名称 and product.商品名称 = T1.商品名称

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