Datatables server-side processing - PHP / PostgreSQL - advanced queries

I´m trying to figure out how to group data from joined table in Datatables server-side PHP script. The data for datatables in prepared by the PHP script using an SSP class modified for postgreSQL connection. The table consists of products and their categories. Everything is working well, but I cannot figure out how to prepare the SELECT statement in order to group product categories per product. To make it easier to understand my problem you can see a setup example below. PostgreSQL DB table structure: Table: products_table ------------------------------------------ id | title | pr_template_id ------------------------------------------ 1 | Product 1 | 1 2 | Product 2 | 2 3 | Product 3 | 3 ------------------------------------------ Table: product_categories_template_relations ------------------------------------------ id | pr_template_id | category_id ------------------------------------------ 1 | 1 | 1 2 | 1 | 2 3 | 2 | 2 4 | 2 | 3 5 | 3 | 1 ------------------------------------------ Table: product_categories ------------------------------------------ category_id | title ------------------------------------------ 1 | Category 1 2 | Category 2 3 | Category 3 ------------------------------------------ Server side script (PHP): <?php $table = <<<EOT ( SELECT [login to view URL], a.pr_template_id, [login to view URL] as producttitle, b.pr_template_id, b.category_id, [login to view URL] as cattitle FROM products_table a LEFT JOIN product_categories_template_relations b ON a.pr_template_id = b.pr_template_id LEFT JOIN product_categories c ON b.category_id = c.category_id ) temp EOT; ?> Current Datatables results: ------------------------------------------ Product ID | Product title | Category ------------------------------------------ 1 | Product 1 | Category 1 1 | Product 1 | Category 2 2 | Product 2 | Category 2 2 | Product 2 | Category 3 3 | Product 3 | Category 1 ------------------------------------------ Datatables results I´m looking for: --------------------------------------------------------- Product ID | Product title | Category --------------------------------------------------------- 1 | Product 1 | Category 1, Category 2 2 | Product 2 | Category 2, Category 3 3 | Product 3 | Category 1 --------------------------------------------------------- So basically I´m currently stuck at Server side script (PHP) and how to formulate the SQL query correctly.