Question

I have the following database tables :

user
    int unsigned id
    varchar      login

group
    int unsigned id
    varchar      label

right
    int unsigned id
    varchar      label

user_group
    int unsigned userId
    int unsigned groupId

user_right
    int unsigned userId
    int unsigned rightId

group_right
    int unsigned groupId
    int unsigned rightId

A right is considered as granted to a group or a user when it’s associated using user_right or group_right tables (respectivly).
I have the following query that is supposed to retrieve an user’s rights from his login :

SELECT DISTINCT `R`.`id`,
                `R`.`label`
FROM `user` `U`,
     `right` `R`,
     `user_right` `UR`,
     `user_group` `UG`,
     `group_right` `GR`
WHERE (`U`.`id` = `UR`.`userId`
       AND `R`.`id` = `UR`.`rightId`
       OR `U`.`id` = `UG`.`userId`
       AND `UG`.`groupId` = `GR`.`groupId`
       AND `R`.`id` = `GR`.`rightId`)
  AND `U`.`login` = 'admin'

When a user is associated to rights and groups, the query does work and returns the right rights. But when a user has no group, the query does not work. If i remove the unused tables (user_group and group_rights), it does work again.

What should i add to my query to avoid this ? Should I add something like “OR some_column IS NULL” ? I’d appreciate if you could also explain me why so i don’t meet this problem again.

Thanks in advance.

Some sample datas :

user (id, login)
1 'admin'

right (id, label)
1 'r1',
2 'r2',
3 'r3'

user_right (id, label)
1 1

Thanks for reading 🙂

Answer 1

First of all, you are using implicit joins, and, the way you wrote your query, they are INNER JOINs. You should change your query to use proper explicit joins, and use LEFT JOINs in there. Something like this:

SELECT DISTINCT `R`.`id`,
                `R`.`label`
FROM `user` `U`
LEFT JOIN `user_right` `UR`
    ON `U`.`id` = `UR`.`userId`
LEFT JOIN `right` `R`
    ON `R`.`id` = `UR`.`rightId`
LEFT JOIN `user_group` `UG`
    ON `U`.`id` = `UG`.`userId`
LEFT JOIN `group_right` `GR`
    ON `UG`.`groupId` = `GR`.`groupId` AND `R`.`id` = `GR`.`rightId`
WHERE `U`.`login` = 'admin'