mysql - SQL 联合查询错误

Question

我正在尝试连接两个计数查询

SELECT COUNT(*) AS total FROM clients WHERE addedby = 1
UNION
SELECT COUNT(*) AS converts FROM clients WHERE addedby = 1 AND status = '6'

返回的是什么

total
4
0

这是正确的数据，我期待的是这个

total     converts
  4           0

Answer 1

您不需要 UNION 查询来执行此操作。 SELECT A UNION SELECT B返回 A 的行，后跟 B 的行(去重；如果您想要来自两个数据集的 all 行，请使用 UNION ALL )。

你想要的是这样的:

select 
    (select count(*) from clients where addedby=1) as total,
    (select count(*) from clients where addedby=1 and status='6') as converts

其他方法是使用 case ... end 表达式，如果 status='6' 则返回 1:

select 
    count(*) from clients, 
    sum(case when status='6' then 1 else 0 end) as converts
from clients