Sometimes it's not that big of a deal. The idea is if you specify only the columns you need, sometimes those columns can be satisfied directly from the index (

Sometimes it's not that big of a deal. The idea is if you specify only the columns you need, sometimes those columns can be satisfied directly from the index (what's known as a covering index) and you don't need to seek around to the various data pages to pull the rest of the columns. InnoDB though uses a clustered indexing scheme, where the rest of the columns are stored in the leaf nodes, so if you query by primary key, all the data is right there -- no extra seeking. Anyway, obviously it's better to only ask for what you need, but it's not the stupidest thing in the world to SELECT with wildcard.