why does this mysql query still run without the proper ON condition -

why does this mysql query still run without the proper ON condition -

when debugging code found 1 of queries causing temp table of mysql run out of memory. found query executing though 'on' status did not have equals match fields. wondering...

what seemed cause horrendous performance lag?

(i ran explain command didn't seem help)

as rudimentary illustration query:

"select testfield foo f left bring together bar b on b.testid testid = 40365";

this because you're joining on status true, means operation bit cartesian product.

i guess tables big plenty cause memory problem.

mysql