how to use the if condition in the sql code example

Example 1: if in sql

SELECT 
  IF(500<1000, "YES", "NO");

Example 2: how to do an if statement in sql server

DECLARE @Course_ID INT = 4

IF (@Course_ID = 4)
Select * from Guru99 where Tutorial_ID = 4
ELSE
Select * from Guru99 where Tutorial_ID != 4