Where do I do this?

[eluser]danmontgomery[/eluser]
This has very little to do with CI, it's basic database functionality.

The query in plain SQL would be:

Code:

SELECT product.*, image.url
FROM product
LEFT JOIN image ON image.product_id = product.id

Assuming you'd want to use CI's active record, that would be:

Code:

$this->db->select('product.*, image.url')->join('image', 'image.product_id = product.id', 'left')->get('product');