Conditional sql WHERE clause based on column values

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:

1. If user is Administrator , then select all users ( Administrators, Managers, Simple Users )
2. Else if user is Manager select all Managers and all Simple Users
3. 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 (eg 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

您可以使用以下代码

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);