sql query to divide a value over different records - sql

Question

Consider the following recordset:
1 1000 -1
2 500 2
3 1000 -1
4 500 3
5 500 2
6 1000 -1
7 500 1
So 3x a number 1000 with -1, total -3.
4x a number 500 with different values
Now I'm in need of a query which divides the sum of code 1000 over the 4 number 500 and removes code 1000.
So the end result would look like:
1 500 1.25
2 500 2.25
3 500 1.25
4 500 0.25
The sum of code 1000 = -3
There's 4 times code 500 in the table over which -3 has to be divided.
-3/4 = -0.75
so the record "2 500 2" becomes "2 500 (2+ -0.75)" = 1.25
etc
As an SQL newbie I have no clue how to get this done, can anyone help?

Answer 1

You can use CTEs to do it "step-wise" and build your solution. Like this:
with sumup as
(
select sum(colb) as s
from table
where cola = 1000
), countup as
(
select count(*) as c
from table
where cola = 500
), change as
(
select s / c as v
from sumup, countup
)
select cola, colb - v
from table, change
where cola = 500
Two things to note:
This might not be the fastest solution, but it is often close.
You can test this code easy, just change to final select statement to select the name of the CTE and see what it is. For example this would be a good test if you are getting a bad result:
with sumup as
(
select sum(colb) as s
from table
where cola = 1000
), countup as
(
select count(*) as c
from table
where cola = 500
), change as
(
select s / c as v
from sumup, countup
)
select * form change

Answer 2

Select col1,(
(Select sum(col2 )
from tab
where col1 =1000)
/
(Select count(*)
from tab
where col1 =500))+Col2 as new_value
From tab
Where col1=500
Here tab, col1,col2 are table name, column with (1000 , 500) value, column with (1,2,3 value)

Answer 3

This will give the results you are after:
DECLARE #T TABLE (ID INT, Number INT, Value INT)
INSERT #T (ID, Number, Value)
VALUES
(1, 1000, -1),
(2, 500, 2),
(3, 1000, -1),
(4, 500, 3),
(5, 500, 2),
(6, 1000,-1),
(7, 500, 1);
SELECT Number, Value, NewValue = Value + (x.Total / COUNT(*) OVER())
FROM #T T
CROSS JOIN
( SELECT Total = CAST(SUM(Value) AS FLOAT)
FROM #T
WHERE Number = 1000
) x
WHERE T.Number = 500;
Inside the cross join we simply get the sum where the number is 1000, this could just as easily be done as a subselect:
SELECT Number, Value, NewValue = Value + ((SELECT CAST(SUM(Value) AS FLOAT) FROM #T WHERE Number = 1000) / COUNT(*) OVER())
FROM #T T
WHERE T.Number = 500;
Or with a variable:
DECLARE #Total FLOAT = (SELECT SUM(Value) FROM #T WHERE Number = 1000);
SELECT Number, Value, NewValue = Value + (#Total / COUNT(*) OVER())
FROM #T T
WHERE T.Number = 500;
Then using the analytic function COUNT(*) OVER() you can count the total number of results that are 500.

Answer 4

And here is another solution:
select number1, value1,
value1
+ (select sum(value1) from table1 where number1=1000)/
(select count(*) from table1 where number1=500) calc_value
from table1 where number1=500
http://sqlfiddle.com/#!6/c68a0/1
I hope I got your question right. Then this is imho the best to read.