sql中的减号函数

Question

SELECT COUNT(DISTINCT CASE WHEN a.caption = 'abc' THEN a.id END) AS "Reject",
       COUNT(DISTINCT CASE WHEN b.caption ='5' THEN b.id END) AS "Dup"
FROM a with (NOLOCK) left outer join
     b re with (NOLOCK)
     On a.id= b.id   

我想在同一个sql查询中获得两个计数的差。当我使用减号函数时，它给我错误：数据类型varchar和varchar在减运算符中不兼容。

Answer 1

它应该像这样：

SELECT COUNT(DISTINCT CASE WHEN a.caption = 'abc' THEN a.id END) AS "Reject",
       COUNT(DISTINCT CASE WHEN b.caption ='5' THEN b.id END) AS "Dup",
       (COUNT(DISTINCT CASE WHEN a.caption = 'abc' THEN a.id END) -
        COUNT(DISTINCT CASE WHEN b.caption ='5' THEN b.id END)
       ) as diff
FROM a LEFT JOIN
     b re
     ON a.id = b.id  ; 

除非您真的知道自己在做什么，否则不要使用WITH (NOLOCK)。您可能会得到不一致的数据。