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GROUP BY Components

SQL Server 2000

The GROUP BY clause contains the following components:

  • One or more aggregate-free expressions. These are usually references to the grouping columns.

  • Optionally, the ALL keyword, which specifies that all groups produced by the GROUP BY clause are returned, even if some of the groups do not have any rows that meet the search conditions.

  • CUBE or ROLLUP.

  • Typically, the HAVING clause is used with the GROUP BY clause, although HAVING can be specified separately.

You can group by an expression as long as it does not include aggregate functions, for example:

SELECT DATEPART(yy, HireDate) AS Year,
       COUNT(*) AS NumberOfHires
FROM Northwind.dbo.Employees
GROUP BY DATEPART(yy, HireDate)

This is the result set.

Year     NumberOfHires
1992     3
1993     3
1994     3

(3 row(s) affected)

In a GROUP BY, you must specify the name of a table or view column, not the name of a result set column assigned with an AS clause. For example, replacing the GROUP BY DATEPART(yy, HireDate) clause with GROUP BY Year is not legal.

You can list more than one column in the GROUP BY clause to nest groups; that is, you can group a table by any combination of columns. For example, this query finds the average price and the sum of year-to-date sales, grouped by type and publisher ID:

USE pubs
SELECT type, pub_id, 'avg' = AVG(price), 'sum' = sum(ytd_sales)
FROM titles
GROUP BY type, pub_id

Here is the result set:

type         pub_id avg                    sum         
------------ ------ ---------------------- ----------- 
business     0736    2.99                  18722       
psychology   0736   11.48                  9564        
mod_cook     0877   11.49                  24278       
psychology   0877   21.59                  375         
trad_cook    0877   15.96                  19566       
UNDECIDED    0877    NULL                  NULL      
business     1389   17.31                  12066       
popular_comp 1389   21.48                  12875       

(8 row(s) affected)

See Also

SELECT

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