mysql中出現 Unknown column ‘xxx‘ in ‘having clause‘

mysql中出現 Unknown column ‘xxx‘ in ‘having clause‘

這是因為在使用group by分組時，后面如果需要再加一個having進行判斷，則所判斷的字段需要在select后面出現

如：

select c.studentNo, c.name, count(coursename)
from courses a, scores b, students c
where a.courseNo = b.courseNo
and b.studentNo = c.studentNo
GROUP BY c.studentNo
having count(coursename) = 5

如果不出現，則會報錯

 

 *代碼只是做演示，結果是有問題的