SQL查询，如何选择开，盘中

Question

我有表名为sessions是select查询返回此：

 
id name state 
-------------------- 
1  n1  open 
2  n2  open 
3  n1  close 
4  n3  open 

我想返回刚才打开的会话的查询。 （n2和n3）。 我试图inner join会话表，自己却没有作品...

Answer 1

试试这个：

SELECT t1.* 
FROM mytable AS t1 
LEFT JOIN mytable AS t2 ON t1.name = t2.name 
      AND t2.state = 'close' 
WHERE t1.state = 'open' AND t2.id IS NULL 

上面的查询将返回所有'open'记录不匹配'close'状态记录。

Demo here

Answer 2

返回，如果状态是打开的，并最迟ID具有相同的名称，但闭合状态的名字：

select distinct name 
from sessions s1 
where state = 'open' 
    and not exists (select 1 from sessions s2 
        where s2.name = s1.name 
        and s2.state = 'close' 
        and s2.id > s1.id)