除非值选择行由另一行

Question

FROM TO  TYPE 
---- ---- ---- 
John Jane Like 
Jill Jane Like 
Jane John Hide 

取消我怎么会写SELECT语句是这样的：

SELECT * FROM table WHERE to='Jane' UNLESS from='Jane' AND type='hide' 

，使得在上表中，它将返回约翰·吉尔，减去约翰因为简选择隐藏约翰，这意味着只有吉尔会被退回。

Answer 1

使用not exists：

select t.* 
from t 
where t.to = 'Jane' and 
     not exists (select 1 
        from t t2 
        where t2.from = t.to and t2.type = 'Hide' 
       );