SQL UPDATE with sub-query that references the same

Question

I'm trying to update a column's value in a bunch of rows in a table using UPDATE. The problem is that I need to use a sub-query to derive the value for this column, and it depends on the same table. Here's the query:

UPDATE user_account student
SET student.student_education_facility_id = (
   SELECT teacher.education_facility_id
   FROM user_account teacher
   WHERE teacher.user_account_id = student.teacher_id AND teacher.user_type = 'ROLE_TEACHER'
)
WHERE student.user_type = 'ROLE_STUDENT';

Ordinarily if teacher and student were in 2 different tables, mysql wouldn't complain. But since they are both using the same table, mysql spews out this error instead:

ERROR 1093 (HY000): You can't specify target table 'student' for update in FROM clause

Is there any way I can force mysql to do the update? I am 100% positive the from clause will not be affected as the rows are updated.

If not, is there another way I can write this update sql to achieve the same affect?

Thanks!

EDIT: I think I got it to work:

UPDATE user_account student
LEFT JOIN user_account teacher ON teacher.user_account_id = student.teacher_id
SET student.student_education_facility_id = teacher.education_facility_id
WHERE student.user_type = 'ROLE_STUDENT';

Answer 1

I get "Error: Invalid use of group function" when I do that.

But this post: mysql query to update field to max(field) + 1

shows an even-more-nested-subselect thing, that works.

Answer 2

UPDATE user_account student

SET (student.student_education_facility_id) = (

   SELECT teacher.education_facility_id

   FROM user_account teacher

   WHERE teacher.user_account_id = student.teacher_id AND teacher.user_type = 'ROLE_TEACHER'

)

WHERE student.user_type = 'ROLE_STUDENT';

Answer 3

I needed this for SQL Server. Here it is:

UPDATE user_account 
SET student_education_facility_id = cnt.education_facility_id
from  (
   SELECT user_account_id,education_facility_id
   FROM user_account 
   WHERE user_type = 'ROLE_TEACHER'
) as cnt
WHERE user_account.user_type = 'ROLE_STUDENT' and cnt.user_account_id = user_account.teacher_id

I think it works with other RDBMSes (please confirm). I like the syntax because it's extensible.

The format I needed was this actually:

UPDATE table1 
SET f1 = cnt.computed_column
from  (
   SELECT id,computed_column --can be any complex subquery
   FROM table1
) as cnt
WHERE cnt.id = table1.id

Answer 4

UPDATE user_account student, (
   SELECT teacher.education_facility_id as teacherid
   FROM user_account teacher
   WHERE teacher.user_account_id = student.teacher_id AND teacher.user_type = 'ROLE_TEACHER'
) teach SET student.student_education_facility_id= teach.teacherid WHERE student.user_type = 'ROLE_STUDENT';

Answer 5

Some reference for you http://dev.mysql.com/doc/refman/5.0/en/update.html

UPDATE user_account student 
INNER JOIN user_account teacher ON
   teacher.user_account_id = student.teacher_id 
   AND teacher.user_type = 'ROLE_TEACHER'
SET student.student_education_facility_id = teacher.education_facility_id

Answer 6

Abstract example with clearer table and column names:

UPDATE tableName t1
INNER JOIN tableName t2 ON t2.ref_column = t1.ref_column
SET t1.column_to_update = t2.column_desired_value

As suggested by @Nico

Hope this help someone.