$sql="select something from something_else";
$res_id=mysql_query($sql);
if (!$res_id) {
	$message  = 'Invalid query: ' . mysql_error() . "\n";
        $message .= 'Whole query: ' . $sql;
        die($message);
}

Dumps whole query so developer can see where is error. However it's potential security issue, exposing SQL commands to attacker. (Recommended to use only during development, replace message code with some custom error text)

Mysql query in PHP with proper error detection

mysql, php

PHP