I have two tables, like this:

tableA: field1, field2
tableB: field1, field2

I've been using mysql on this machine for a long time. A couple of days ago I entered this query from phpMyAdmin:

select * from tableA left join tableB on tableB.field1=tableA.field1 or tableB.field1=tableA.field2

At that point, a mysqld process showed up in my Mac's activity monitor, and it sucked up 95+% of the CPU forever. The query never returns. Since then, all hell is breaking loose on my Mac. mysql keeps telling me that it can't talk to the servers, MAMP can't reliably start and stop mysql, and strangely, the Mac is running super-hot although nothing is running on it now.

Please, someone, tell me you've seen exactly this before and you know exactly how to fix it. I'm totally stuck.