Does the number of columns returned affect the speed of a query?

Question

If I have two queries

SELECT Id, Forename, Surname
FROM Person
WHERE PersonName Like(‘%frank%’)

And

SELECT *
FROM Person
WH         


        

Answer 1

the only time i use "select *" is not event really a "select *"

specifically:

select count(*) from table

is not that same as

select count(ID) from table

the first returns the number of rows in the table
but the second returns the number of rows with a NOT NULL ID value.

a subtle distinction but worth remembering.