MySQL查询与

Question

我有两个表l & C它们由两个字段l.mID和c.mID的C表包含三种类型的记录cs, ls, & vs与我的查询链接列计数我需要从L和作为查询有一部分选择所有记录三栏显示cs, ls & vs的总数;

到目前为止，我使用的是外部联接：

SELECT l.*, COUNT(*) FROM l LEFT OUTER JOIN c ON c.mID = l.mID WHERE l.mID = 2 

但是，这只是一个附加柱采用了全总的任何帮助将是巨大的感谢。

Answer 1

您可以在计数使用CASE声明：

select 
    l.* 
    ,COUNT(CASE WHEN c.type = 'cs' then 1 END) as cscount 
    ,COUNT(CASE WHEN c.type = 'ls' then 1 END) as lscount 
    ,COUNT(CASE WHEN c.type = 'vs' then 1 END) as vscount 
from l 
left outer join c on c.mID = l.mID 
where l.mID = 2 

Answer 2

select 
    l.* 
    ,sum(c.type = 'cs') as cscount 
    ,sum(c.type = 'ls') as lscount 
    ,sum(c.type = 'vs') as vscount 
from l 
left outer join c on c.mID = l.mID 
where l.mID = 2