Mysql – Commands like CREATE, GRANT, DROP always return “0 rows affected”

Here's mysql_num_rows:

int mysql_num_rows ( resource $result ) 

Retrieves the number of rows from a result set. This command is only valid for statements like SELECT or SHOW that return an actual result set. To retrieve the number of rows affected by a INSERT, UPDATE, REPLACE or DELETE query, use mysql_affected_rows().

And here's mysql_affected_rows:

int mysql_affected_rows ([ resource $link_identifier = NULL ] )

Get the number of affected rows by the last INSERT, UPDATE, REPLACE or DELETE query associated with link_identifier.

Notice that the input types are different: the first wants a result set, from which it counts the number of rows returned; the second wants a db handle. That makes sense, though, because when you INSERT (or UPDATE, DELETE, REPLACE) a row, you typically don't want a result set -- you just want to know if it succeeded or failed, or how many rows it updated/replaced/deleted.

Limit does have an impact on how many rows are selected/affected. 543 is just the number of rows which match the joins and the where clause.