Arrays and php

[Dynamo]

Hi,

I have one problem with arrays. I have database tables like these:

Students
-student_id
-name
-grade

and

StudentGroups
-group_id
-members (student_id's in one column like this way "63,65,68,69")

Now if I want average grades with groups how I must handle arrays and database queries?

BR,D

[Weedpacket]

With a lot of fluffing around that wouldn't be necessary if you redesigned your tables.

Student
- student_id
- name
- grade
- other student stuff

Group
- group_id
- other group stuff

Student_Group
- group_id
- student_id

If there is no "other group stuff" then it's still two tables, but it still needs fixing.

Student
- student_id
- name
- grade
- other student stuff

Student_Group
- group_id
- student_id

In both Student_Group tables, there is only one student ID in the student_id field. If there are several students in the same group, there are several rows in the table.

Average grade for group $group:

Select
	avg(Student.grade)
from
	Student,
	Student_Group
where
	Student.student_id=Student_Group.student_id
	and
	Student_Group.group_id=$group

[jheitz]

Definitely not a good idea to have a field like your members one where you hold student id's separated by commas. This goes against the principle of relational databases... but just imagine how painful it would be to maintain (delete existing IDs, etc...)