Conditional sql WHERE clause based on column values - mysql

Question

I have a table that stores users. Every user has an ID, a Name and an Access Level. The three possible Access Levels are Administrator, Manager and Simple User.
What I want is to conditionally select from this table based on the Access Level value. I demonstrate the logic bellow:
If user is Administrator, then select all users (Administrators, Managers, Simple Users)
Else if user is Manager select all Managers and all Simple Users
Else if user is Simple User select only himself
Is that possible?

Answer 1

Providing Access Level is an integer that increases with the actual access level:
Administrator = 3
Manager = 2
User = 1
Then
SELECT * FROM USERS
WHERE ACCESS_LEVEL <= (SELECT ACCESS_LEVEL FROM USERS WHERE ID = #ID)
And just switch the less than sign to greater than if it is opposite.
Applies to SQL-server
EDIT: To get what you want you can use something like this:
SELECT id,name FROM users where ID = #id
UNION DISTINCT
SELECT id, name from users where access_level <=
(select case when access_level = 1 then 0 else access_level end
from users where id = #id)
With a query like this you will select all users at your current access_level or lower.
Only exception if your access_level is 1 (e.g. normal user), then only your own user is selected.

Answer 2

In Oracle the concept is known as Row Level Security. See articles such as this or this to get you started.

Answer 3

You can use following code
If(access_level=='administrator'){ str query = 'select * from users';}else if(access_level=='manager'){ str query = 'select * from users where access_level!="administrator"'; }else{ str query = 'select * from users where access_level="users"'; }

Answer 4

Might be a little overkill, but the following stored procedure can be used to achieve what you want:
DROP procedure IF EXISTS `listAccessibleUsers`;
DELIMITER $$
CREATE PROCEDURE `listAccessibleUsers`(IN user_id INT)
BEGIN
DECLARE u_access_level INT;
-- Select the user access level
SELECT access_level
FROM users
WHERE users.id = user_id
INTO u_access_level;
-- Result for simple users
IF u_access_level = 1 THEN
SELECT id, name, access_level
FROM users
WHERE users.id = user_id;
-- Result for admistrators and managers
ELSE
SELECT id, name, access_level
FROM users
WHERE access_level <= u_access_level;
END IF;
END$$
DELIMITER ;
Example calling code:
CALL listAccessibleUsers(200);