ORACLE EXSIST 練習

exists （sql 返回結果集為真）
notexists (sql 不返回結果集為真）

如下：
表A

表B
 

表A和表B是１對多的關係 A.ID => B.AID

 

select a.id from A where exists (select a.id from b where a.id = b.aid);

 

select a.id from Awhere  not exists (      select a.id from  b where a.id = b.aid  );

 

條件查詢

  select *    from A   where exists (select a.id            from b           where a.id = b.aid             and b.name != 'b3');

select a.id  from A where not exists (select a.id from b where a.id = b.aid  and b.name != 'b3');

 三個表聯合exist

母表

子表

又子表

 

查詢語句

select name from C
where exists (
      select * from b where b.id = c.bid and exists (
             select * from a where a.id = b.aid
      )
);

 

 查詢結果