What's the most efficient way to check if a record exists in Oracle?

Question

A)

select decode(count(*), 0, \'N\', \'Y\') rec_exists
from (select \'X\'
      from dual
      where exists (select \'X\'
                    from sales
           


        

Answer 1

SELECT 'Y' REC_EXISTS             
FROM SALES                       
WHERE SALES_TYPE = 'Accessories'

The result will either be 'Y' or NULL. Simply test against 'Y'

Answer 2

select decode(count(*), 0, 'N', 'Y') rec_exists 
      from sales 
      where sales_type = 'Accessories'; 

Answer 3

Simply get a count of the record(s) you're looking for. If count > 0 then record(s) exist.

    DECLARE
    rec_count NUMBER := 0;

    BEGIN

    select count(*) 
    into rec_count  
    from EMPLOYEETABLE  
    WHERE employee_id = inEMPLOYEE_ID  
    AND department_nbr = inDEPARTMENT_NBR;  


    if rec_count > 0 then  
       {UPDATE EMPLOYEETABLE}
    else  
       {INSERT INTO EMPLOYEETABLE}  
    end if;  

    END;

Answer 4

select case 
            when exists (select 1 
                         from sales 
                         where sales_type = 'Accessories') 
            then 'Y' 
            else 'N' 
        end as rec_exists
from dual;