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WHERE SalesOrderID IN (43660, 43670, 43672)
GROUP BY SalesOrderID;
This gets us what we were looking for:
SalesOrderID
------------ -----------
43660 2
43670 6
43672 9
(3 row(s) affected)
Chapter 3: The Foundation Statements of T-SQL
As you would expect, the SUM function returns totals — but totals of what? We can easily supply an alias
for our result. Let’s modify our query slightly to provide a column name for the output:
SELECT SalesOrderID, SUM(OrderQty) AS TotalOrderQty
FROM Sales.SalesOrderDetail
WHERE SalesOrderID IN (43660, 43670, 43672)
GROUP BY SalesOrderID;
This gets us the same basic output, but also supplies a header to the grouped column:
SalesOrderID TotalOrderQty
------------ -------------
43660 2
43670 6
43672 9
(3 row(s) affected)
If you’re just trying to get some quick results, then there really is no need to alias the grouped column as
we’ve done here, but many of your queries are going to be written to supply information to other elements
of a larger program. The code that’s utilizing your queries will need some way of referencing your grouped
column; aliasing your column to some useful name can be critical in that situation. We’ll examine aliasing
a bit more shortly.
If we didn’t supply the GROUP BY clause, the SUM would have been of all the values in all of the rows for
the named column. In this case, however, we did supply a GROUP BY, and so the total provided by the
SUM function is the total in each group.
Note that when using a GROUP BY clause, all the columns in the SELECT list must
either be aggregates (SUM, MIN/MAX, AVG, and so on) or columns included in the
GROUP BY clause. Likewise, if you are using an aggregate in the SELECT list, your
SELECT list must only contain aggregates, or there must be a GROUP BY clause.
We can also group based on multiple columns. To do this we just add a comma and the next column
name. Let’s say, for example, that we’re looking for the number of orders each salesperson has taken for
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