mysql - 在 where 子句中使用带有 CASE 的别名列名

Question

如何修复此查询？我收到以下错误:

Unknown column 'count_of_confirmed_rec' in 'where clause'

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，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' 看起来也可能不适合左连接。

要测试 where 语句中 count_of_confirmed_rec 的值，您需要将除 WHERE 语句之外的所有内容放入子查询中，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