subtracting two diff columns

[cancer10]

Hi

I am confused how to do this.

I have two tables and each table has an "Amount" colum.


I need to sum up all the rows for column "Amount" in table A and sum up all the rows for column "Amount" in table B

and then subtract those two colums.

Here is what I am doing:

select tableA.city, sum(tableA.amount)  - sum(tableB.amount)
from tableB,tableA
where 
tableB.city='Hyderabad' and 
tableB.city=tableA.city
group by tableB.city

Say: tableA Has the following data for column "Amount" and city=Hyderabad:

111
5
10

AND tableB Has the following data for column "Amount" and city=Hyderabad:

6
5

Now, my above query should do the following:

Sum all amounts for tableA, which comes to 126
Sum all amounts for tableB, which comes to 11


So 126 - 11 = 115

But I get the result 219

Any idea wots going on and how to fix it?


Thanx

[smadeira]

You are getting Table A summed more than once because of your join. get rid of the subtraction of the sum()s and just print sum(a) and sum(b) and run the query to see how the joins are causing things to be double counted.

select tableA.city, 
    sum(tableA.amount), 
    sum(tableB.amount)
from 
    tableB,tableA
where 
    tableB.city='Hyderabad' and 
    tableB.city=tableA.city
group by 
    tableB.city

[guido2004]

Joining these two tables on city, will give the following result:

111  6
111  5
  5  6
  5  5
 10  6
 10  5

This gives 252 - 33 = 219

[cancer10]

Joining these two tables on city, will give the following result:

111  6
111  5
  5  6
  5  5
 10  6
 10  5

This gives 252 - 33 = 219

Wots the solution then?

[cancer10]

You are getting Table A summed more than once because of your join. get rid of the subtraction of the sum()s and just print sum(a) and sum(b) and run the query to see how the joins are causing things to be double counted.

select tableA.city, 
    sum(tableA.amount), 
    sum(tableB.amount)
from 
    tableB,tableA
where 
    tableB.city='Hyderabad' and 
    tableB.city=tableA.city
group by 
    tableB.city

What I am doing is incorrect and there is a way?

OR

Is it something not possible in one query?

Thanx

[r937]

Wots the solution then?

obviously, the solution is: don't join

I need to sum up all the rows for column "Amount" in table A and sum up all the rows for column "Amount" in table B

and then subtract those two colums.

SELECT ( SELECT SUM(Amount) FROM tableA )
     - ( SELECT SUM(Amount) FROM tableB ) AS difference

[cancer10]

obviously, the solution is: don't join

SELECT ( SELECT SUM(Amount) FROM tableA )
     - ( SELECT SUM(Amount) FROM tableB ) AS difference

That worked, but can it also show the cities also incase there are more then one city?

[r937]

i'm sorry, that solution works for the question you posted

if you change the question, then the solution has to change too -- obviously

please explain what you mean by "more than one city"

[cancer10]

i'm sorry, that solution works for the question you posted

if you change the question, then the solution has to change too -- obviously

please explain what you mean by "more than one city"

Sorry about that.

See, I might have multiple cities in both tableA and tableB.

I want to do a sum of all rows for column "Amount" for each city in tableA and then do a sum of all rows for column "Amount" for each city in tableA
then subtract the amount from both tables city wise.





Thanx



EDIT: So that it looks like


City | Difference
---------------------
City A | 55
City B | 22
City C | 543
City D | 212

[r937]

I want to do a sum of all rows for column "Amount" for each city in tableA and then do a sum of all rows for column "Amount" for each city in tableA
then subtract the amount from both tables city wise.

SELECT a.city
     , a.total
     , b.total
     , a.total - b.total AS difference
  FROM ( SELECT city
              , SUM(amount) AS total
           FROM tableA
         GROUP
             BY city ) AS a
LEFT OUTER
  JOIN ( SELECT city
              , SUM(amount) AS total
           FROM tableB
         GROUP
             BY city ) AS b
    ON b.city = a.city