mixing AND & OR in an sql statement

[sde]

i'm having trouble mixing AND & OR in an SQL query.

how would i do this:

select game_id from tictactoe where winner IS NOT NULL and p1_id='$userid' or p2_id='$userid' order by game_id desc limit 10

i need it to select a row where the winner is not null, .. but either p1_id or p2_id can equal $userid

this doesn't work for some reason

[abc123]

brackets

x and (y or z)