在 mysql WHERE 子句中使用 GROUP_CONCAT 和 FIND_IN_SET

Question

我有這個查詢，並想使用學生電子郵件從表中獲取約會數據，但它收到此錯誤Unknown column 'stu' in 'where clause'

select a.*, GROUP_CONCAT(e.value) as stu FROM wp_ea_appointments a join
wp_ea_fields e on a.id = e.app_id WHERE a.date > DATE('2019-02-14') AND
FIND_IN_SET('jan@gmail.com' , stu ) GROUP BY a.id

Answer 1

FIND_IN_SET條件應該包含在HAVING語句而不是WHERE語句中，因為您要在分組后過濾數據

SELECT a.*, 
    GROUP_CONCAT(e.value) as stu 
FROM wp_ea_appointments a 
JOIN wp_ea_fields e ON a.id = e.app_id 
WHERE a.date > DATE('2019-02-14')
GROUP BY a.id
HAVING FIND_IN_SET('jan@gmail.com', stu) 

Answer 2

您可以嘗試使用子查詢

select * from
(
select a.*, GROUP_CONCAT(e.value) as stu FROM wp_ea_appointments a join
wp_ea_fields e on a.id = e.app_id WHERE a.date > DATE('2019-02-14') 
GROUP BY a.id
)A where FIND_IN_SET('jan@gmail.com' , stu ) 

Answer 3

使用HAVING子句，但要正確表達邏輯：

SELECT a.*, GROUP_CONCAT(e.value) as stu
FROM wp_ea_appointments a JOIN
     wp_ea_fields e 
     ON a.id = e.app_id
WHERE a.date > DATE('2019-02-14')
HAVING SUM( e.value = 'jan@gmail.com' ) > 0;

沒有理由使用字符串連接來檢查值是否存在。 字符串比較更昂貴且不太清楚。