How to Sum particular values in a column in Microsoft SQL Server? - sql-server

Question

I'm kinda new to this and I have been stuck on this for a while now.
Example:
Col1 Col2 Col3
A | H | 1
A | I | 2
A | J | 3
B | J | 4
B | K | 5
C | L | 6
How can I sum 'Col3' but only for particular values. For example sum up the values in 'Col3' where the letters in 'Col1' are in the same row as 'Col3'. So A = 6 (1+2+3) and B = 9 (4+5) and C = 6
So you get this:
Col1 Col2 Col3
A | H | 6
A | I | 6
A | J | 6
B | J | 9
B | K | 9
C | L | 6
This is what I had so far:
SELECT Col1, Col2, SUM(Col3)
FROM Table1
GROUP BY Col1, Col2;
Thanks

Answer 1

Just to elaborate on my comment.
You can use the window function sum() over()
Example
Declare #YourTable Table ([Col1] varchar(50),[Col2] varchar(50),[Col3] int) Insert Into #YourTable Values
('A','H',1)
,('A','I',2)
,('A','J',3)
,('B','J',4)
,('B','K',5)
,('C','L',6)
Select Col1
,Col2
,Col3 = sum(Col3) over (partition by Col1)
From #YourTable
Returns
Col1 Col2 Col3
A H 6
A I 6
A J 6
B J 9
B K 9
C L 6

Answer 2

Just as another way you can do this way also using join and SUM (Transact-SQL)
function.
create table TestTable (Col1 varchar(5)
, Col2 varchar(5)
, Col3 int)
insert into TestTable Values
('A', 'H', 1),
('A', 'I', 2),
('A', 'J', 3),
('B', 'J', 4),
('B', 'K', 5),
('C', 'L', 6)
SELECT tblA.Col1
,tblA.Col2
,tblB.Col3
FROM (
SELECT Col1
,Col2
FROM TestTable
) tblA
INNER JOIN (
SELECT Col1
,sum(Col3) AS Col3
FROM TestTable
GROUP BY Col1
) tblB ON tblA.Col1 = tblB.Col1
Live Demo

Answer 3

There are a number of ways to write data aggregation queries like this. Which to use depends on what your final results need to look like. Just to go over some basics, I’ll go over several methods here.
The simplest is to use a WHERE clause:
SELECT Col1, sum(Col3)
from MyTable
where Col1 = 'A'
This will produce a single row of data:
Col1 Col3
A | 6
To produce sums for all of the distinct values in ColA, you would use GROUP BY:
SELECT Col1, sum(Col3)
from MyTable
group by Col1
This will produce three rows of data:
Col1 Col3
A | 6
B | 9
C | 6
The above samples are pretty straightforward and basic SQL examples. It is actually a bit difficult to produce the result set from your example, where you include Col2 and show the summation, because Col2 is not part of the data aggregation. Several ways to do this:
Using a subquery:
SELECT
mt.Col1
,mt.Col2
,sub.SumCol3 Col3
from MyTable mt
inner join (select
Col1
,sum(Col3) SumCol3
from MyTable
group by Col1) sub
on sub.Col1 = mt.Col1
Using a common table expression:
WITH cteSub
as (select
Col1
,sum(Col3) SumCol3
from MyTable
group by Col1)
select
mt.Col1
,mt.Col2
,cteSub.SumCol3 Col3
from MyTable mt
inner join cteSub
on ctesub.Col1 = mt.Col1
And, perhaps the most obscure and obtuse, using aggregation fucntions with partitioning:
SELECT
Col1
,Col2
,sum(Col3) over (partition by Col1) Col3
from MyTable
Thorough and complete discussions of all the above tactics (better than anything I'd write) can be found online, by searching for "SQL" plus the appropriate term (aggregation, subquery, CTE, paritioning functions). Good luck!