Why does mysql_query() return TRUE with a SELECT statement?

Question

According to the manual of mysql_query() and to everything I know about this function that I used so many times, it can either return a resource or FALSE if the

Answer 1

You haven't mentioned data lengths but you should check to see if this is called by an exceeding of max_allowed_packet.

When a MySQL client or the mysqld server receives a packet bigger than max_allowed_packet bytes, it issues a Packet too large error and closes the connection. With some clients, you may also get a Lost connection to MySQL server during query error if the communication packet is too large.

[...]

Both the client and the server have their own max_allowed_packet variable, so if you want to handle big packets, you must increase this variable both in the client and in the server.

http://dev.mysql.com/doc/refman/5.5/en/packet-too-large.html

Not sure how mysql_query return value is affected by this but it's worth investigating. Setting it in my.cnf to see if it fixes the problem would be the best place to start.