Fastest way to determine if record exists

Question

As the title suggests... I\'m trying to figure out the fastest way with the least overhead to determine if a record exists in a table or not.

Sample query:

Answer 1

Nothing can beat -

SELECT TOP 1 1 FROM products WHERE id = 'some value';

You don't need to count to know if there is a data in table. And don't use alias when not necessary.

Answer 2

You can also use

 If EXISTS (SELECT 1 FROM dbo.T1 WHERE T1.Name='Scot')
    BEGIN
         --<Do something>
    END 

ELSE    
     BEGIN
       --<Do something>
     END

Answer 3

SELECT TOP 1 products.id FROM products WHERE products.id = ?; will outperform all of your suggestions as it will terminate execution after it finds the first record.

Answer 4

SELECT CASE WHEN EXISTS (SELECT TOP 1 *
                         FROM dbo.[YourTable] 
                         WHERE [YourColumn] = [YourValue]) 
            THEN CAST (1 AS BIT) 
            ELSE CAST (0 AS BIT) END

This approach returns a boolean for you.

Answer 5

For those stumbling upon this from MySQL or Oracle background - MySQL supports the LIMIT clause to select a limited number of records, while Oracle uses ROWNUM.

Answer 6

create or replace procedure ex(j in number) as
i number;
begin
select id into i from student where id=j;
if i is not null then
dbms_output.put_line('exists');
end if;
exception
   when no_data_found then
        dbms_output.put_line(i||' does not exists');

end;