How do I do an IF in Microsoft SQL SELECT query?

Question

I am an absolute beginner in SQL. Example: I want to do a query to select people whose names begin with X if the result is 0, I want to select people whose names begin with Y.

How do I do this? Thanks.

Answer 1

I interpret the question as: show names starting with Y if no names starting with X are found. This solution will be fast as it will short-cut the exists from the moment 1 record is found

if exists(select * from table where name like 'X%')
  begin
    select * from table where name like 'X%'
  end
else
  begin
    select * from table where name like 'Y%'
  end

Ideally the name column is indexed for this to work well.