Unknown Column in Where Clause : Mysql Update Query

Question

This is my update query:

update grade 
  set grade='A'
where (select assignment*0.3+midExam*0.35+finalExam*0.35 as FINALSCORE 
       from taking) >= 85 
  and taking.student_id = grade.student_id 
  and taking.subject_id = grade.subject-id;

and the result is below

Unknown column 'taking.student_id' in 'where clause'

What am i doing wrong?

Answer 1

The table taking is inside a subquery then is not visible outside the subquery

for your need you should use an update with join

update grade 
INNER JOIN taking ON taking.student_id=grade.student_id
       and taking.subject_id=grade.subject_id 
         and taking.assignment*0.3+taking.midExam*0.35+taking.finalExam*0.35 >= 85
set grade='A'

for a general solution

you could try adding a case when for each grade

update grade 
INNER JOIN taking ON taking.student_id=grade.student_id
       and taking.subject_id=grade.subject_id          
set grade = (case when taking.assignment*0.3+taking.midExam*0.35+taking.finalExam*0.35 >= 85 THEN  'A'
              when taking.assignment*0.3+taking.midExam*0.35+taking.finalExam*0.35 between 60.0 and 84.9 THEN 'B'
              ELSE 'C' END)