使用 COUNT() 的 MySQL 查询返回字段等于 COUNT 值的记录

Question

我有以下查询，效果很好:

SELECT *, COUNT(*) FROM attendance, cohort 
WHERE 
attendance.cohort_fk = cohort.cohort_pk 
AND 
attendance.cohort_fk = '$cohort' 
AND 
YEAR(attendance.attended) = '$year'
GROUP BY attendance.person_id ASC

在表 cohort 中，有一个 int 列 'attendance_pass'。现在我想要另一个与上面类似的查询，它只返回 COUNT(*) FROM attendance 等于 cohort.attendance_pass 的记录。例如。

SELECT *, COUNT(*) FROM attendance, cohort 
WHERE 
attendance.cohort_fk = cohort.cohort_pk 
AND 
attendance.cohort_fk = '$cohort' 
AND 
YEAR(attendance.attended) = '$year'
AND 
COUNT() = cohort.attendance_pass
GROUP BY attendance.person_id ASC

如何修改第二个查询以仅获取这些记录？

Answer 1

你需要使用HAVING

SELECT *, COUNT(*) FROM attendance, cohort 
WHERE 
attendance.cohort_fk = cohort.cohort_pk 
AND 
attendance.cohort_fk = '$cohort' 
AND 
YEAR(attendance.attended) = '$year'

GROUP BY attendance.person_id ASC

HAVING COUNT(*) = cohort.attendance_pass