SQL: How to properly check if a record exists

Question

While reading some SQL Tuning-related documentation, I found this:

SELECT COUNT(*) :

• Counts the number of rows.
• Often is improper

Answer 1

I would prefer not use Count function at all:

IF [NOT] EXISTS ( SELECT 1 FROM MyTable WHERE ... )
     

---

For example if you want to check if user exists before inserting it into the database the query can look like this:

IF NOT EXISTS ( SELECT 1 FROM Users WHERE FirstName = 'John' AND LastName = 'Smith' )
BEGIN
    INSERT INTO Users (FirstName, LastName) VALUES ('John', 'Smith')
END