Question

假设我有一个查询

create table friends (
userid int,
friend int,
status int 
);

知道查询的哪一部分正在执行是否可行？例如，下面的示例应该告诉1是否满足(userid=1 and friend=2)或告诉2是否执行(friend=2 and userid=1 )部分。

//wrong example
select status,@var 
  from friends 
 where @var:=(userid=1 and friend=2) 
    or @var:=(friend=2 and userid=1 );

Answer 1

我想这就是你要找的东西：

SELECT status,
    CASE 
    WHEN (userid=1 and friend=2) THEN 'opt1'
    WHEN (friend=2 and userid=1) THEN 'opt2'
END AS 'var'
FROM friends 
WHERE userid IN (1, 2) 
    OR friend IN (1, 2)

如何知道查询的哪个部分已执行

1 个答案: