SELECT * runs slower than listing columns (even when you want everything). If you don’t want every column, you save on network time, disk I/O, CPU, and memory. Every resource SQL Server touches! Even when you need every column though, SELECT * can create issues in JOIN predicates, and causes more CPU to be used. You should instead list just the columns you need, all columns if necessary.

What’s the point of this T-SQL Tips is a series that I have been sharing with developers and analysts who write their own T-SQL and design their own databases. The goal is to make those things better through a fun and educational blurb.