Why is SELECT * considered harmful?

Question

Why is SELECT * bad practice? Wouldn\'t it mean less code to change if you added a new column you wanted?

I understand that SELECT COUNT(*)

Answer 1

If you really want every column, I haven't seen a performance difference between select (*) and naming the columns. The driver to name the columns might be simply to be explicit about what columns you expect to see in your code.

Often though, you don't want every column and the select(*) can result in unnecessary work for the database server and unnecessary information having to be passed over the network. It's unlikely to cause a noticeable problem unless the system is heavily utilised or the network connectivity is slow.