Question

如果我有查询，例如：

select column1, (
    select count(*) from table2
) as some_count
from table1
where column1 = 'foo'

我可以在where子句中使用column1，但是如果我尝试添加

and some_count > 0

然后我收到some_count不存在的错误。我怎样才能在where子句中使用它？

Answer 1

使用HAVING

select column1, (
    select count(*) from table2
) as some_count
from table1
HAVING some_count > 0

Answer 2

原样，唯一的方法是使用派生表：

SELECT x.*
  FROM (select column1, 
               (select count(*) from table2) as some_count
          from table1
         where column1 = 'foo') x
 WHERE x.some_count > 0

你是否意识到没有相关性，some_count将为返回的每一行返回相同的值？

在MySQL where子句中使用生成的列

2 个答案: