title: MYSQL Limit Occurences of a particular column value
body: <p>Pulling some coupons from a database. Each coupon has a <code>merchantid</code> column that contains the id for the merchant for which the coupon belongs too.</p>
  
  <p>I'm trying to construct a query that pulls 5 coupons, but I only want 1 coupon per <code>merchantid</code>. I don't want multiple coupons with the same <code>merchantid</code>.</p>