mySql unknown column

Question

I have the following query

    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 

and I get the following error

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

Do not know how to solve this since the column is in the select statement

Answer 1

your derived column count_absent is processed in the SELECT clause, which is processed AFTER the WHERE clause, and so is therefore not available. It would be available if you wrapped the whole query in an outer SELECT, to be able to access the derived column.

i.e.

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