mySql未知列

Question

我有以下查询

    SELECT 
     s.name, 
     s.surname, 
     s.id_nr, 
     s.student_nr, 
     s.createdate, 
     s.enddate, 
     (SELECT count(*) FROM Student_Attendance WHERE absent = 1) AS count_absent 
    FROM 
     Student AS s, 
     Student_Contact AS sc, 
     Student_Payment AS p, 
     Student_Courses AS scou, 
     Modules AS m, 
     Student_Certificate AS scer, 
     Student_Results AS sr, 
     Lecturer_Profile AS l, 
     Lecturer_Comments AS lc, 
     Student_Attendance AS sa, 
     Student_Training AS t 
    WHERE s.s_id = sc.s_id 
    AND s.s_id = p.s_id 
    AND s.s_id = scou.s_id 
    AND scou.c_id = m.c_id 
    AND s.s_id = scer.s_id 
    AND s.s_id = sr.s_id 
    AND s.s_id = lc.s_id 
    AND lc.l_id = l.l_id 
    AND s.s_id = sa.s_id 
    AND LOWER(s.name) = 'andile' 
    AND LOWER(s.surname)  = ' orson vulture' 
    AND s.id_nr = 8403125062671 
    AND LOWER(sc.race) = 'white' 
    AND sc.gender = 1 
    AND LOWER(sc.area) = 'gauteng' 
    AND p.payment_type = 1 
    AND s.student_nr = 203087506 
    AND scou.c_id = 1 AND sc.age = 23 
    AND scer.certificate_number = 3424234 
    AND sr.result = 32 
    AND l.l_id= 1 
    AND count_absent = 3 
    AND LOWER(s.branch) = 'pretoria' 
    AND LOWER(s.campus_name) = 'pretoria' 
    AND LOWER(sc.kin_name) = 'self' 
    AND t.s_id = s.s_id 
    AND t.sp_id = 1 

我收到以下错误

CDbCommand failed to execute the SQL statement: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'count_absent' in 'where clause'

由于列在select语句中

，因此不知道如何解决这个问题

Answer 1

派生列count_absent在SELECT子句中处理，该子句在WHERE子句之后处理，因此不可用。如果将整个查询包装在外部SELECT中，则可以访问派生列。

即

select * from (
SELECT 
 s.name, 
 s.surname, 
 s.id_nr, 
 s.student_nr, 
 s.createdate, 
 s.enddate, 
 (SELECT count(*) FROM Student_Attendance WHERE absent = 1) AS count_absent 
FROM 
 Student AS s, 
 Student_Contact AS sc, 
 Student_Payment AS p, 
 Student_Courses AS scou, 
 Modules AS m, 
 Student_Certificate AS scer, 
 Student_Results AS sr, 
 Lecturer_Profile AS l, 
 Lecturer_Comments AS lc, 
 Student_Attendance AS sa, 
 Student_Training AS t 
WHERE s.s_id = sc.s_id 
AND s.s_id = p.s_id 
...
AND t.s_id = s.s_id 
AND t.sp_id = 1
) as x where count_absent = 3

Answer 2

我不确定你要在这里完成什么，但请注意，给count_absent的嵌入式查询除了“absent = 1”之外不使用任何标准。因此，无论您正在查看哪个学生，您都将获得缺少= 1的所有student_attendance记录的计数。我怀疑你想把它限制在所选学生的student_attendance记录中。

另外，您可以调查“join”子句。这将使您的查询更容易理解当时加入where旧样式。