Sql: How to properly check if a record exists

Question

Reading some SQL Tuning documentation I found this:

Select count(*) :

- Counts the number of rows

- Often is improperly used to verify the existence of a record

Is Select count(*) really that bad?

What's the proper way to verify the existence of a record?

Answer 1

Use the code given below:

Query 1:

SELECT 1

FROM table_name

WHERE key = value;

Otherwise, you can use this query:

Query 2:

SELECT COUNT(1)

FROM table_name

WHERE key = value;

Note: The first query will give you either no result or zero result, and in the second query count should be either zero or one.