update … from语句
测试环境准备
create table #table1 ( id int , name varchar(20) ); go create table #table2 ( id int , name varchar(20) ); go insert into #table1 ( id, name ) values ( 1, 'a' ), ( 2, null ), ( 3, 'c' ), ( 4, 'd' ), ( 5, 'e' ); insert into #table2 ( id, name ) values ( 1, 'a1' ), ( 2, 'b1' ), ( 3, 'c1' );
1、目标表可以加表别名(目标表在from子句)
----join连接方式(推荐) update a set a.name = b.name from #table1 a inner join #table2 b on b.id = a.id where a.name is null;
----子查询方式 update a set a.name = ( select b.name from #table2 b where a.id = b.id ) from #table1 a where a.name is null;
2、目标表不能加表别名(目标表不在from子句):
update #table1 set #table1.name = b.name from #table2 b where #table1.id = b.id and #table1.name is null;
--或 update #table1 set name = ( select b.name from #table2 b where #table1.id = b.id ) where name is null;
3、Merge更新
merge #table1 a --要更新的目标表 using #table2 b --源表 on a.id = b.id and a.name is null--更新条件(即主键) when matched --如果匹配,更新 then update set a.name = b.name when not matched then insert values ( id, name ); --如果两个条件都不匹配,插入。此语句必须以分号结束
清除测试数据
select * from #table1; select * from #table2; drop table #table1; drop table #table2;