select * from tb1 a where =(select min(id2) from tb1 where id1=a.id1)其中的a该如何理解?
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select*fromtb1awhere=(selectmin(id2)fromtb1whereid1=a.id1)其中的a该如何理解?select*fromtb1awhere=(selectmin(
select * from tb1 a where =(select min(id2) from tb1 where id1=a.id1)其中的a该如何理解?
select * from tb1 a where =(select min(id2) from tb1 where id1=a.id1)
其中的a该如何理解?
select * from tb1 a where =(select min(id2) from tb1 where id1=a.id1)其中的a该如何理解?
A 为TB1表或视图的别名,这里表示TB1,一般用来在表较多,表名较长,表名有重复时使用.
提取列名时,需加表名前缀时,如表有别名,用别名代替,如这里的A.ID1
select * from tb1 a where =(select min(id2) from tb1 where id1=a.id1)
select * from tb1 a where =(select min(id2) from tb1 where id1=a.id1)其中的a该如何理解?
关于select tb1.a,tb2.a from a,这样选出来的两个a列是排列组合,比如a中有3条数据,b中有4条.则选出12条,怎么写,可以使选出来的数据 tb1.a就是3条,tb2.a就是4条
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