SQL Server 用一张表的数据更新另一张表的数据(转载) |
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文章二:SQL 用一个表的数据更新另一张表
https://blog.51cto.com/alun51cto/2392062?source=dra 用表B的数据(B1列,B2)更新表A的A1,A2列 SQL Server: update A SET A.A1 = b.B1,A.A2=B.A2 FROM A ,B WHERE A.ID1 = B.ID1 and A.ID2 = B.ID2;Access: update A, B set A.A1 = B.B1,A.A2=B.B2 where A.ID1 = B.ID1 and A.ID2 = B.ID2; --或 update A INNER JOIN B ON A.ID1 = B.ID1 AND A.ID2= B.ID2 SET A.A1 = B.B1,A.A2=B.B2;通过一条SQL语句一次更新多条数据.SQL语句写法略有不同,如下: 方法一: Update T1 set dc=(select dc1 from t2 where T1.A=T2.A1 AND T1.B=T2.B1) WHERE T1.AID in ( SELECT AID FROM T1 INNER JOIN T2 ON t1.A=T2.A1 AND T1.B=T2.B1 )注:在我标我红色的in地方如果把'in'换成'='将出错,但在下面的B种写法里就可以换成'=',变成C方法写法. 方法二: Update T1 set dc=(select dc1 from t2 where T1.A=T2.A1 AND T1.B=T2.B1) WHERE T1.AID in ( SELECT T1.AID FROM T2 WHERE t1.A=T2.A1 AND T1.B=T2.B1 )方法三: Update T1 set dc=(select dc1 from t2 where T1.A=T2.A1 AND T1.B=T2.B1) WHERE T1.AID = ( SELECT T1.AID FROM T2 WHERE t1.A=T2.A1 AND T1.B=T2.B1 )方法四: Update T1 set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1) WHERE T1.A = ( SELECT T1.A FROM T2 WHERE T1.A=T2.A1 AND T1.B=T2.B1 )方法五: Update T1 set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1) WHERE T1.A = ( SELECT T2.A1 FROM T2 WHERE T1.A=T2.A1 AND T1.B=T2.B1 )方法六: Update T1 set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1) WHERE T1.A in ( SELECT T2.A1 FROM T2 WHERE T1.A=T2.A1 AND T1.B=T2.B1 )注:如果在上面方法改写成如下的写法将会出错。 Update T1 set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1) WHERE T1.A in ( SELECT T1.A FROM T1 INNER JOIN T2 ON t1.A=T2.A1 AND T1.B=T2.B1 )此种方法将会更新掉所有符合T1.A in ()这个条件的数据,所以是不正确的, 所以不能这样写。 方法七: Update T1 set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1 AND T1.DC=T2.DC1) FROM T1, T2 WHERE T1.A=T2.A1 AND T1.B=T2.B1方法八: Update T1 set T1.dc=T2.dc1 FROM T1 INNER JOIN T2 ON T1.A=T2.A1 AND T1.B=T2.B1 WHERE t1.A=T2.A1 AND T1.B=T2.B1方法九: Update T1 set T1.dc=T2.dc1 FROM T1, T2 WHERE T1.A=T2.A1 AND T1.B=T2.B1请特别注意以上方法中我用红色标记上的代码写法。 总节:虽然是一条简单的更新语名但也有多种写法,且每种写法各有优缺点。 大家是否还有更简单的写法或者更容易理解的写法?如果有请提出来一起讨论,谢谢! 说明测试环境:以上代码在MSSQL2005中验证是可行的. 注:此处我用灰色标记的部分可以去掉。 |
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