Question

I have a mysql table where user permissions are stored as a bitmask:

|user   | permissions |
| Admin | 31          |
| User  | 13          |

           16 8  4  2  1
Admin ->   1  1  1  1  1  -> 16 + 8 + 4 + 2 + 1 -> 31
User  ->   0  1  1  0  1  ->  8 + 4 + 1 -> 13

Now I want to add a permission for every user with an sql query.
Let’s say I want to add the permission 16 for everyone without modifying another bit.

 UPDATE users SET permission = ????

How do I do this?

Answer 1

To add permission 16, you just say

UPDATE users SET permission = permission | 16;

The bitwise OR operator will turn bits on. To turn them off, use a AND operation with the complement of the bit you want off:

UPDATE users SET permission = permission & ~16