Question

Basically, I have two tables, admin_privilege and admin_roll_privilege. I’m trying to write a query to get every row from admin_privilege, and if there is a row in admin_roll_privilege with a matching admin_privilege_id AND a matching admin_roll_id, to set a new column to 1. So far, I have this:

  SELECT ap.*, 
    IF(arp.admin_privilege_id IS NULL,0,1) AS has_privilege
  FROM admin_privilege ap LEFT JOIN admin_roll_privilege arp
    ON ap.admin_privilege_id=arp.admin_privilege_id
  WHERE arp.admin_roll_id=3 
    OR arp.admin_roll_id IS NULL;

This works in every case except where there are no matching rows admin_roll_privilege.

See Example:

+---------------+--------------------+
| admin_roll_id | admin_privilege_id |
+---------------+--------------------+
|             1 |                  2 |
|             1 |                  3 |
+---------------+--------------------+

+--------------------+------------------------+
| admin_privilege_id | admin_privilege_name   |
+--------------------+------------------------+
|                  1 | Access Developer Tools |
|                  4 | Edit System Settings   |
|                  2 | Edit User Profiles     |
|                  3 | Resolve Challenges     |
+--------------------+------------------------+

Querying for WHERE admin roll id=1 works as expected:

+--------------------+------------------------+---------------+
| admin_privilege_id | admin_privilege_name   | has_privilege |
+--------------------+------------------------+---------------+
|                  1 | Access Developer Tools |             0 |
|                  4 | Edit System Settings   |             0 |
|                  2 | Edit User Profiles     |             1 |
|                  3 | Resolve Challenges     |             1 |
+--------------------+------------------------+---------------+

But, if i query for admin_roll_id=3, i only get two rows returned:

+--------------------+------------------------+---------------+
| admin_privilege_id | admin_privilege_name   | has_privilege |
+--------------------+------------------------+---------------+
|                  1 | Access Developer Tools |             0 |
|                  4 | Edit System Settings   |             0 |
+--------------------+------------------------+---------------+

How can I get this query to return all 4?

Edit: This is what ended up working, moving the condition to the on clause:

SELECT ap.*, 
    IF(arp.admin_privilege_id IS NULL,0,1) AS has_privilege
  FROM admin_privilege ap LEFT JOIN admin_roll_privilege arp
    ON (ap.admin_privilege_id=arp.admin_privilege_id AND arp.admin_roll_id=1)

Answer 1

Move the appropriate conditions from the WHERE clause to the ON clause.