在where子句中使用帶CASE的別名列名稱

Question

如何解決此查詢？

Unknown column 'count_of_confirmed_rec' in 'where clause'

的MySQL查詢：下面我錯誤地接收

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，你的計算count_of_confirmed_rec子查詢不與外部查詢相關;因此它會爲查詢的所有返回行提供相同的值。不知道這是你想不想的。

其次，您的條件d.col_1 = 'value'也看起來可能錯位爲左連接。

對於您的WHERE語句測試count_of_confirmed_rec的價值，你需要把一切都只是在一個子查詢的WHERE語句，並適用於由查詢（未經測試）返回的行的條件：

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