Sum values from multiple rows into one row

Question

In SQL Server 2012, I have a table my_table that has columns state, month, ID, and sales.

My goal is to merge different rows

Answer 1

Considering there should be an index on column id, this query would be a better solution:

select state, month, id, sum(sales) Total
from yourtable
group by id, state, month
order by id

Answer 2

Unless I am missing something in the requirements, why not just use an aggregate function with a GROUP BY:

select state, month, id, sum(sales) Total
from yourtable
group by state, month, id
order by id

See SQL Fiddle with Demo

The result is:

| STATE |   MONTH | ID | TOTAL |
--------------------------------
|    FL |    July |  1 | 10000 |
|    FL |    June |  1 | 21000 |
|    CA |   April | 32 |  2000 |
|    MI |   April | 32 | 13000 |
|    TX | January | 50 |  1000 |