Mysql Slow when join query running increaed
With MyISAM, an INSERT/UPDATE/DELETE will request an exclusive lock, and have to wait for any SELECTs to finish. If another SELECT comes in after the write, then it will be blocked waiting for the write to get its lock and finish its action.

That is, one simple write can snowball into the mess you are seeing.

Changing to InnoDB is likely to avoid the problem, since locks are taken at the row level, not the table level.

Let's see the EXPLAIN for your SELECT (and provide one that does not have syntax errors).  Plus tell us how big the table is.  And SHOW CREATE TABLE for each relevant table.

Speeding up the query will help avoid the locks.