在where子句中使用别名列名和CASE

Question

如何解决此查询？ 我收到以下错误：

“ where子句”中的未知列“ count_of_confirmed_rec”

MySQL查询：

SELECT 
(SELECT COUNT(a.col_1)FROM table_1 a
JOIN table 2 b ON a.col_id= b.col_id) count_of_confirmed_rec,
c.col_1,
FROM table_3 c
LEFT JOIN table_4 d ON c.col_id = d.col_id 
WHERE d.col_1 = 'value'
AND c.col_1 = CASE count_of_confirmed_rec
WHEN 0 THEN 0 ELSE 1 END

Answer 1

首先，您用于计算count_of_confirmed_rec的子查询与外部查询不相关； 因此，它将为查询的所有返回行提供相同的值。 不确定这是否是您想要的。

其次，您的条件d.col_1 = 'value'对于左联接也可能放错了位置。

为了在where语句中测试count_of_confirmed_rec的值，您需要将WHERE语句以外的所有内容放在子查询中，并将条件应用于查询返回的行（未经测试）：

select count_of_confirmed_rec, c_col_1 from (
SELECT (SELECT COUNT(a.col_1)FROM table_1 a JOIN table 2 b ON a.col_id= b.col_id) count_of_confirmed_rec, c.col_1 as c_col_1
FROM table_3 c LEFT JOIN table_4 d ON c.col_id = d.col_id 
WHERE d.col_1 = 'value'
) SQ
where c_col_1 = CASE count_of_confirmed_rec WHEN 0 THEN 0 ELSE 1 END