get the opposite results from a SELECT query

Question

these are my tables:

`room`(roomID,roomNum)  
`customer`(customerID,Surname,etc)  
`contract`(contractID,roomID,weekNum)  
`paymen`t(paymentID,customerID,contractID,YearKoino)

and when i use the following query:

`select` room.roomnum  
`from` payment,contract,room,customer  
`where` payment.contractID = contract.contractID  
`and` contract.roomID=room.roomID  
`and` customer.customerID=payment.customerID  
`and` contract.weeknum='40'  
`and` payment.YearKoino='2007' ;

the results i am getting are:

+---------+  
| roomnum |  
+---------+  
| Δ-12    |  
| Γ-22    |  
| Α-32    |  
| Γ-21    |  
| Δ-11    |  
| Ε-12    |  
| Γ-31    |  
| Ε-22    |  
| Α-22    |  
| Δ-12    |  
| Γ-12    |  
+---------+  
11 rows in set

what i want to do is to run a query that gives me the exact opposite results(roomnums in table room that are not in table payment).This can be done by comparing the roomum results from the above query with the column roomnum in the room table.some of my efforts so far :

`Select` room.roomnum  
`from` room  
`where` NOT EXISTS  
(`select` room.roomnum  
`from` payment,contract,room,customer  
`where` payment.contractID = contract.contractID  
`and` contract.roomID=room.roomID  
`and` customer.customerID=payment.customerID  
`and` contract.weeknum='40'  
`AND` payment.YearKoino='2007');  
Empty set

and

`SELECT` *
`FROM` customer a
`LEFT OUTER JOIN` payment b
`on` a.customerID=b.customerID
`where` a.customer is null;

i also tried to replace the "NOT EXISTS" with the "NOT IN" but in vain.I have read that the best way to do that is by using the "left join".well i can do it when i have to compare to simple tables.but in my example i have to compare a column with a column that is in a join of tables...

any advice would be appreciated.

score 4 · Accepted Answer · answered Nov 21 '12 at 21:10

I am not sure why your not in didn't work.

This should work (using not in with table name aliases):

   Select r1.roomnum 
   from room AS r1
   where r1.roomnum NOT IN 
       (select r2.roomnum 
        from payment,contract,room as r2,customer 
        where payment.contractID = contract.contractID
        and contract.roomID=r2.roomID 
        and customer.customerID=payment.customerID 
        and contract.weeknum='40' 
        AND payment.YearKoino='2007');

that worked perfect.i havent used aliases and that was my mistake.thanx a lot for your help!!! — amon, Nov 21 '12 at 21:28

score 1 · Answer 2 · answered Nov 21 '12 at 21:11

Of course you must correlate your NOT EXISTS query with your main query

Select 
  roomnum 
from 
  room main
where 
  NOT EXISTS (
   select 1 
   from   payment
          inner join contract on payment.contractID = contract.contractID
          inner join room     on contract.roomID = room.roomID 
          inner join customer on customer.customerID = payment.customerID 
   where  contract.weeknum='40' 
          and payment.YearKoino='2007'
          and room.roomnum = main.roomnum  -- < correlation to main query
);

Also, learn SQL-92 style joins. Nobody does old style joins anymore.

get the opposite results from a SELECT query

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