Question

I have following stored procedure:

CREATE PROCEDURE testProc(IN p_idProject INTEGER)
BEGIN
DECLARE nowTime DATETIME;
SET @nowTime = NOW();

     SELECT 
         idCustomer 
     FROM NextCalls WHERE @nowTime-nextCall = 
         (SELECT MAX(@nowTime - nextCall) 
          FROM NextCalls 
          WHERE idProject = p_idProject AND nextCall < @nowTime) 
     LIMIT 1;
END $$

There is index set on nextCall column. Unfortunately it’s being logged into mysql-slow.log file as a query that is not using indexes properly. This procedure is used very, very often and I would be really happy to avoid bad indexing. Is it possible to rewrite to achieve that?

Answer 1

You are just selecting the oldest nextCall. There is no need to perform any calculations, you can just use ORDER BY:

SELECT idCustomer 
FROM NextCalls 
WHERE idProject = p_idProject AND nextCall < CURRENT_TIMESTAMP
ORDER BY nextCall
LIMIT 1