Question

I have:

• a coupons table with a column called owner_id and id
• and an owners table with a column called id and website_url.

I’d like to get owners.website_url using only coupons.id (which is provided in a php variable $coupon_id.

Here’s my best shot:

SELECT owners.website_url
FROM owners o
LEFT JOIN coupons c
ON o.id = c.owner_id
WHERE c.id='$coupon_id'
LIMIT 1

Is this correct? I put LIMIT 1 beacause there are many coupons per owner.

Answer 1

It looks correct, but it’s pointless to use a LEFT JOIN there since you are filtering away the failed joins in your WHERE clause. Just use JOIN.

You also shouldn’t need the LIMIT clause since all coupons should have unique ids (assuming that id is a primary key) and each coupon has only one owner.