Question

Please consider this Query:

SELECT tesd.State_Code,
   tesd.City_Code,
   tesd.Row_ID,
   tesd.Qsno,
   tesd.Total_Period,
   tesd.Current_Period,
   tesd.Week,
   tesd.Block_No,
   tesd.Family_ID,
   tesd.Line_ID,
   tesd.Page_ID
   INTO #tmp
FROM   Specification_Master tesm
   INNER JOIN Specification_Details tesd
        ON  tesd.Master_Id = tesm.Id
WHERE  tesm.[Year] = 2000
   AND tesm.[Month] = 10
   AND tesd.City_Code IN ('001')

I queried some data from 2 tables and insert them in #tmp .then I want to select data from 2 other tables and check one of that tables has values in #tmp tbale:

SELECT *
FROM   tbl_Details D
   INNER JOIN tbl_Master tem
        ON  D.ID_Master = tem.Id
WHERE  D.Period <= 5
 AND EXISTS (
           SELECT Row_ID
           FROM   #tmp tm
           WHERE  tm.Current_Period > 1
                  AND tm.State_Code = tem.State_Code
                  AND tm.City_Code = tem.City_Code
                  AND tm.Qsno = tem.Qsno
       )
   AND D.[Status] > 2 

when I run this query I got just one row but when I change EXISTS to NOT EXISTS I got more rows.I run this query seperatly :

SELECT Row_ID
           FROM   #tmp tm,tbl_Master tem 
           WHERE  tm.Current_Period > 1
                  AND tm.Ostan_Code = tem.State_Code
                  AND tm.City_Code = tem.City_Code
                  AND tm.Porseshname_ID = tem.Qsno

and it returns 30 rows. Why Exists has this such behaivior ?

Answer 1

Exists returns a Boolean value based on the results of the subquery. It matters not if there are 1 or 30 rows returned. The number of rows you are retrieving is based on the select * statement, not the Exists clause.