IF Clause in Left Join

Hi, I really need some help. I'm trying to use an IF statement in a multi-table left join. I'm joining four tables (customers, contents, courses & locations). In the contents table I have two fields, product_id and value_id that relate to different values in different tables depending upon the value in the product_type field. If product_type='course' then the product_id and value_id relate to the courses and locations table, but if product_type='other' then the product_id and value_id relate to the product and prices table. I have two options: 1. Match only the courses and locations where product_type='course' and NULL values if relating to the product and prices table. 2. Or change the query (and fields) if the product_type='other' to use the product and prices table. I'm using Mysql 4.3. Here's what I had that worked, but it did not take into account that the values in the product_id and value_id fields relate to different tables if the product_type != 'course'... $command = " CREATE TABLE $table[name] "; $command.= " SELECT $fields1, $fields2, $fields3 "; $command.= " FROM (($table[customers] AS c "; $command.= " LEFT JOIN $table[contents] AS o ON o.order_id = c.order_id) "; $command.= " LEFT JOIN $table[courses] AS t ON o.product_id = t.id) "; $command.= " LEFT JOIN $table[locations] AS l ON o.value_id = l.id "; Here's my first attempt at employing the IF statement within the Mysql query: $command = " CREATE TABLE $table[name] "; $command.= " SELECT $fields1, $fields2, $fields3 "; $command.= " FROM ($table[customers] AS c "; $command.= " LEFT JOIN $table[contents] AS o ON o.order_id = c.order_id) "; $command.= " IF((o.product_type='course'), (LEFT JOIN $table[courses] AS t ON o.product_id = t.id LEFT JOIN $table[locations] AS l ON o.value_id = l.id), NULL )"; Finally, if there is a way for me to override a column value using PHP during the execution of the mysql query, then I could accept a simpler solution. If I can use PHP to check the value of product_type and then get the values of product_id and value_id from an array... All I need to know is how to inject php values into my simple query. Say: SELECT field1, field2, field3, IF(o.product_type='course', $product_name[$product_id] ,NULL) AS product, field5 FROM table1 as a, table2 as o; The key point here is that I must be able to output the final results of my query to a new table. I'd be extremely grateful for any help anyone can provide. Thanks. Keith