Question

I have two sql queries as following

SELECT rc.stateId,rs.stateName FROM
(SELECT DISTINCT cityid FROM HolidayPackageCity) AS hpc
 INNER JOIN 
 (SELECT cityid,stateid FROM RegCity WHERE countryCode='IN' AND stateId IS NOT NULL) AS rc
ON hpc.cityId=rc.cityId
INNER JOIN
RegState AS rs
ON rc.stateId=rs.stateId

vs

SELECT DISTINCT rc.stateId,rs.stateName 
FROM HolidayPackageCity AS hpc
INNER JOIN 
  RegCity  AS rc
  ON hpc.cityId=rc.cityId
  INNER JOIN
    RegState AS rs
    ON rc.stateId=rs.stateId
WHERE rc.countryCode='IN' AND rc.stateId IS NOT NULL

In first query first i filter the data of a particular table then apply joining and in second table first i apply joins then i apply where condition to filter the data.
The thing i want to know is which one is faster from both of that and why.

Answer 1

Second query is faster, because optimizer would first filter table with where clause, and then create internal temp table which later use for join. Conclusion – better solution is join with tables which contains smaller data sets.

By the way, optimizer easier deal with second query, which no contains subqueries.