select * vs select column

Question

If I just need 2/3 columns and I query SELECT * instead of providing those columns in select query, is there any performance degradation regarding more/less I/O

Answer 1

This immediately makes me think of a table I was using which contained a column of type blob; it usually contained a JPEG image, a few Mbs in size.

Needless to say I didn't SELECT that column unless I really needed it. Having that data floating around - especially when I selected mulitple rows - was just a hassle.

However, I will admit that I otherwise usually query for all the columns in a table.