Simple MySQL Issue

Simple MySQL Issue

OK I have a column with a W or L to designate a win or loss. I want to
count all the wins and losses, and get a win percentage.
SELECT banner_name, count(win_loss) as wins
FROM drop_log
where win_loss = 'W'
group by banner_name
This gives me all the teams and how many wins they have. How would I tweak
this to have another column for losses and another one for ratio. MySQL
appears to have different syntax rules than SQL Server 2008.