在 mysql WHERE 子句中使用 GROUP_CONCAT 和 FIND_IN_SET

Question

我有这个查询，并想使用学生电子邮件从表中获取约会数据，但它收到此错误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条件应该包含在HAVING语句而不是WHERE语句中，因为您要在分组后过滤数据

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

您可以尝试使用子查询

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，但要正确表达逻辑：

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;

没有理由使用字符串连接来检查值是否存在。 字符串比较更昂贵且不太清楚。