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SQL join 用于把来自两个或多个表的行结合起来
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join
2021-12-31 11:17:53
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hlcx
sql
join
# 下图展示了 LEFT JOIN、RIGHT JOIN、INNER JOIN、OUTER JOIN 相关的 7 种用法  # 例子 ```js create table #a (af1 int) insert into #a select 1 insert into #a select 2 create table #b (bf1 int) insert into #b select 2 insert into #b select 3 select 'lwft join' x,a.*,b.* from #a a left join #b b on a.af1=b.bf1 select 'right join' x,a.*,b.* from #a a right join #b b on a.af1=b.bf1 select 'inner join' x,a.*,b.* from #a a inner join #b b on a.af1=b.bf1 select 'lwft join b is null' x,a.*,b.* from #a a left join #b b on a.af1=b.bf1 where b.bf1 is null select 'right join a is null' x,a.*,b.* from #a a right join #b b on a.af1=b.bf1 where a.af1 is null select 'full outer join' x,a.*,b.* from #a a full outer join #b b on a.af1=b.bf1 select 'full outer join a or b null' x,a.*,b.* from #a a full outer join #b b on a.af1=b.bf1 where a.af1 is null or b.bf1 is null drop table #a drop table #b ```
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