Writing SQL Query to query and update same table - sql

Question

I am not very friendly with SQL so I need to write a SQL update/delete query on a table. The requirement is as below.
Table A:
Col1(PK) Col2 Col3 Quantity
1 Code1
Value1 5
2 Code2 Value2 2
3 Code1 Value1 3
4 Code3 Value3 8
Considering above table, in which there are multiple rows with same value for Col2 and Col3. I want to write a query which will delete duplicate combination of Col2 and Col3 and sum the Quantity for the resulting record.
The result should be like this:
Col1(PK) Col2 Col3 Quantity
1 Code1
Value1 8
2 Code2 Value2 2
4 Code3 Value3 8

Answer 1

You will need to do this in two parts, and if you want to ensure the integrity of the data, the two parts should be wrapped in a transaction.
The first part updates the required rows' Quantity, the second deletes the now duplicated rows.
BEGIN TRANSACTION
UPDATE TableA
SET Quantity=upd.Quantity
FROM TableA a
INNER JOIN (
SELECT MIN(Col1) AS Col1, SUM(Quantity) AS Quantity
FROM TableA
GROUP BY Col2, Col3
) upd
ON a.Col1 = upd.col1
;WITH DELETES
AS
(
SELECT Col1,ROW_NUMBER() OVER (PARTITION BY Col2,Col3 ORDER BY Col1) rn
FROM TableA
)
DELETE FROM TableA WHERE Col1 IN (
SELECT Col1 FROM DELETES WHERE rn>1
)
COMMIT TRANSACTION
Live example: http://www.sqlfiddle.com/#!3/9efa9/7
(EDIT: Updated to fix issue noted in comments)

Answer 2

Use this:
select *
from (select *, sum(Quantity) over (partition by col2,col3) as Quantity
from tableA
) t

Answer 3

One option would be to just SELECT the result set you want into a new table, and then drop the previous table:
CREATE TABLE A_new(Col1 INT PRIMARY KEY,
Col2 varchar(255),
Col3 varchar(255),
Quantity INT);
INSERT INTO A_new (Col1, Col2, Col3, Quantity)
SELECT MIN(Col1) AS Col1, Col2, Col3, SUM(Quantity) AS Quantity
FROM A
GROUP BY Col2, Col3
Next you can drop table A and rename A_new to A:
DROP TABLE A
sp_rename A_New, A

Answer 4

For the first Update step(Assume that Table A has the name of Table_1) :
Update Table_1 set Quantity = t.total
from Table_1 As p inner join
(select Min(Col1) as Col1,SUM(quantity) as total from Table_1 group by Col2,Col3) as t
on p.Col1=t.Col1
this will update each row that has more than 1 row with its SUM of quantity.
then you can delete the same row which its code2 has the same value with :
WITH CTE AS(
SELECT
RN = ROW_NUMBER()OVER(PARTITION BY Col2,Col3 ORDER BY Col2,Col3)
FROM Table_1
)
DELETE FROM CTE WHERE RN > 1;
Sorry, I thought that Col2 would always be the same with Col3. *I have edited my statements. If you got more than 1 row, it could Delete all, except the first row.

Answer 5

Please execute the below query:
SELECT
Col2,
Col3,
SUM(Quantity)
FROM table_1
GROUP BY
Col2,
Col3