Yes, the number of fields in
SELECT
statement may affect on query performance.
There's tons of web pages where you can find many useful information, for example:
Query Performance[
^]
7 performance tips for faster SQL queries[
^]
More you'll find via using Google, Bing or any other search engine.
I'd suggest to use SearchBox in the right-top corner on this page to filter CodePorject Knowledge Base.