Question

在previous question中我询问如果user_id与每个表中的记录匹配，如何从3个不同的表返回id。 sql -

select
    (select id from bla_facebook_accts where user_id = user.user_id) as facebook,
    (select id from bla_linked_in_accts where user_id = user.user_id) as linkedin,
    (select id from bla_twitter_accts where user_id = user.user_id) as twitter
from
    (select 12 user_id) user

效果很好，但是我希望每个select语句返回一个表是否有一个记录来返回一个新行，如果一个表有多个记录，则返回多行。

Answer 1

你走了。这也将返回信息的源表。

SELECT'facebook' source, id FROM bla_facebook_accts WHERE (user_id = 12)
UNION
SELECT 'linkedin' source, id FROM bla_linked_in_accts WHERE (user_id = 12)
UNION
SELECT'twitter' source, id FROM bla_twitter_accts WHERE (user_id = 12)

Answer 2

我相信您想要使用UNION构造：

select id from bla_facebook_accts where user_id = 12
UNION 
select id from bla_linked_in_accts where user_id = 12
UNION 
select id from bla_twitter_accts where user_id = 12

为每条记录返回一个新行

2 个答案: