SELECT - OVER#
Determines the partitioning and ordering of a rowset before the associated window function is applied. That is, the OVER clause defines a window or user-specified set of rows within a query result set. A window function then computes a value for each row in the window. You can use the OVER clause with functions to compute aggregated values such as moving averages, cumulative aggregates, running totals, or a top N per group results.
Syntax#
OVER ( [ PARTITION BY value_expression ] [ order_by_clause ] )
Arguments#
PARTITION BY
Divides the query result set into partitions. The window function is applied to each partition separately and computation restarts for each partition.
value_expression
Specifies the column by which the rowset is partitioned. value_expression can only refer to columns made available by the FROM clause. value_expression cannot refer to expressions or aliases in the select list. value_expression can be a column expression, scalar subquery, scalar function, or user-defined variable.
<ORDER BY clause>
Defines the logical order of the rows within each partition of the result set. That is, it specifies the logical order in which the window functioncalculation is performed.
order_by_expression
Specifies a column or expression on which to sort. order_by_expression can only refer to columns made available by the FROM clause. An integer cannot be specified to represent a column name or alias.
ASC | DESC
Specifies that the values in the specified column should be sorted in ascending or descending order. ASC is the default sort order. Null values are treated as the lowest possible values.
Examples#
A. Using the OVER clause with the ROW_NUMBER function#
The following example shows using the OVER clause with ROW_NUMBER function to display a row number for each row within a partition.
The ORDER BY clause specified in the OVER clause orders the rows in each partition by the column SalesYTD.
The ORDER BY clause in the SELECT statement determines the order in which the entire query result set is returned.
USE AdventureWorks2012;
SELECT ROW_NUMBER() OVER(PARTITION BY PostalCode ORDER BY SalesYTD DESC) AS "Row Number",
p.LastName, s.SalesYTD, a.PostalCode
FROM Sales.SalesPerson AS s
INNER
JOIN Person.Person AS p
ON s.BusinessEntityID = p.BusinessEntityID
INNER
JOIN Person.Address AS a
ON a.AddressID = p.BusinessEntityID
WHERE TerritoryID IS NOT NULL
AND SalesYTD <> 0
ORDER BY PostalCode;
Here is the result set.
Row Number LastName SalesYTD PostalCode
--------------- ----------------------- --------------------- ----------
1 Mitchell 4251368.5497 98027
2 Blythe 3763178.1787 98027
3 Carson 3189418.3662 98027
4 Reiter 2315185.611 98027
5 Vargas 1453719.4653 98027
6 Ansman-Wolfe 1352577.1325 98027
1 Pak 4116871.2277 98055
2 Varkey Chudukatil 3121616.3202 98055
3 Saraiva 2604540.7172 98055
4 Ito 2458535.6169 98055
5 Valdez 1827066.7118 98055
6 Mensa-Annan 1576562.1966 98055
7 Campbell 1573012.9383 98055
8 Tsoflias 1421810.9242 98055
B. Using the OVER clause with aggregate functions#
The following example uses the OVER clause with aggregate functions over all rows returned by the query.
In this example, using the OVER clause is more efficient than using subqueries to derive the aggregate values.
USE AdventureWorks2012;
SELECT SalesOrderID, ProductID, OrderQty
, SUM(OrderQty) OVER(PARTITION BY SalesOrderID) AS Total
, AVG(OrderQty) OVER(PARTITION BY SalesOrderID) AS "Avg"
, COUNT(OrderQty) OVER(PARTITION BY SalesOrderID) AS "Count"
, MIN(OrderQty) OVER(PARTITION BY SalesOrderID) AS "Min"
, MAX(OrderQty) OVER(PARTITION BY SalesOrderID) AS "Max"
FROM Sales.SalesOrderDetail
WHERE SalesOrderID IN(43659,43664);
Here is the result set:
SalesOrderID ProductID OrderQty Total Avg Count Min Max
------------ ----------- -------- ----------- ----------- ----------- ------ ------
43659 776 1 26 2 12 1 6
43659 777 3 26 2 12 1 6
43659 778 1 26 2 12 1 6
43659 771 1 26 2 12 1 6
43659 772 1 26 2 12 1 6
43659 773 2 26 2 12 1 6
43659 774 1 26 2 12 1 6
43659 714 3 26 2 12 1 6
43659 716 1 26 2 12 1 6
43659 709 6 26 2 12 1 6
43659 712 2 26 2 12 1 6
43659 711 4 26 2 12 1 6
43664 772 1 14 1 8 1 4
43664 775 4 14 1 8 1 4
43664 714 1 14 1 8 1 4
43664 716 1 14 1 8 1 4
43664 777 2 14 1 8 1 4
43664 771 3 14 1 8 1 4
43664 773 1 14 1 8 1 4
43664 778 1 14 1 8 1 4
The following example shows using the OVER clause with an aggregate function in a calculated value.
USE AdventureWorks2012;
GO
SELECT SalesOrderID, ProductID, OrderQty
,SUM(OrderQty) OVER(PARTITION BY SalesOrderID) AS Total
,CAST(1. * OrderQty / SUM(OrderQty) OVER(PARTITION BY SalesOrderID)
*100 AS DECIMAL(5,2))AS "Percent by ProductID"
FROM Sales.SalesOrderDetail
WHERE SalesOrderID IN(43659,43664);
GO
Here is the result set. Notice that the aggregates are calculated by SalesOrderID
and the Percent by ProductID is calculated for each line of each SalesOrderID.
SalesOrderID ProductID OrderQty Total Percent by ProductID
------------ ----------- -------- ----------- --------------------
43659 776 1 26 3.85
43659 777 3 26 11.54
43659 778 1 26 3.85
43659 771 1 26 3.85
43659 772 1 26 3.85
43659 773 2 26 7.69
43659 774 1 26 3.85
43659 714 3 26 11.54
43659 716 1 26 3.85
43659 709 6 26 23.08
43659 712 2 26 7.69
43659 711 4 26 15.38
43664 772 1 14 7.14
43664 775 4 14 28.57
43664 714 1 14 7.14
43664 716 1 14 7.14
43664 777 2 14 14.29
43664 771 3 14 21.4
43664 773 1 14 7.14
43664 778 1 14 7.14
(20 row(s) affected)
C. Producing a moving average and cumulative total#
The following example uses the AVG and SUM functions with the OVER clause to provide a moving average
and cumulative total of yearly sales for each territory in the Sales.SalesPerson table.
The data is partitioned by TerritoryID and logically ordered by SalesYTD.
This means that the AVG function is computed for each territory based on the sales year.
Notice that for TerritoryID, there are two rows for sales year 2005 representing the two sales people with sales that year.
The average sales for these two rows is computed and then the third row representing sales for the year 2006 is included in the computation.
USE AdventureWorks2012;
GO
SELECT BusinessEntityID, TerritoryID
, DATEPART(yy,ModifiedDate) AS SalesYear
, CONVERT(varchar(20),SalesYTD,1) AS SalesYTD
, CONVERT(varchar(20),AVG(SalesYTD) OVER (PARTITION BY TerritoryID
ORDER BY DATEPART(yy,ModifiedDate)
),1) AS MovingAvg
, CONVERT(varchar(20),SUM(SalesYTD) OVER (PARTITION BY TerritoryID
ORDER BY DATEPART(yy,ModifiedDate)
),1) AS CumulativeTotal
FROM Sales.SalesPerson
WHERE TerritoryID IS NULL OR TerritoryID < 5
ORDER BY TerritoryID,SalesYear;
Here is the result set:
BusinessEntityID TerritoryID SalesYear SalesYTD MovingAvg CumulativeTotal
---------------- ----------- ----------- -------------------- -------------------- --------------------
274 NULL 2005 559,697.56 559,697.56 559,697.56
287 NULL 2006 519,905.93 539,801.75 1,079,603.50
285 NULL 2007 172,524.45 417,375.98 1,252,127.95
283 1 2005 1,573,012.94 1,462,795.04 2,925,590.07
280 1 2005 1,352,577.13 1,462,795.04 2,925,590.07
284 1 2006 1,576,562.20 1,500,717.42 4,502,152.27
275 2 2005 3,763,178.18 3,763,178.18 3,763,178.18
277 3 2005 3,189,418.37 3,189,418.37 3,189,418.37
276 4 2005 4,251,368.55 3,354,952.08 6,709,904.17
281 4 2005 2,458,535.62 3,354,952.08 6,709,904.17
(10 row(s) affected)
In this example, the OVER clause does not include PARTITION BY. This means that the function will be applied to all rows returned by the query. The ORDER BY clause specified in the OVER clause determines the logical order to which the AVG function is applied. The query returns a moving average of sales by year for all sales territories specified in the WHERE clause. The ORDER BY clause specified in the SELECT statement determines the order in which the rows of the query are displayed.
SELECT BusinessEntityID, TerritoryID
, DATEPART(yy,ModifiedDate) AS SalesYear
, CONVERT(varchar(20),SalesYTD,1) AS SalesYTD
, CONVERT(varchar(20),AVG(SalesYTD) OVER (ORDER BY DATEPART(yy,ModifiedDate)
),1) AS MovingAvg
, CONVERT(varchar(20),SUM(SalesYTD) OVER (ORDER BY DATEPART(yy,ModifiedDate)
),1) AS CumulativeTotal
FROM Sales.SalesPerson
WHERE TerritoryID IS NULL OR TerritoryID < 5
ORDER BY SalesYear;
Here is the result set:
BusinessEntityID TerritoryID SalesYear SalesYTD MovingAvg CumulativeTotal
---------------- ----------- ----------- -------------------- -------------------- --------------------
274 NULL 2005 559,697.56 2,449,684.05 17,147,788.35
275 2 2005 3,763,178.18 2,449,684.05 17,147,788.35
276 4 2005 4,251,368.55 2,449,684.05 17,147,788.35
277 3 2005 3,189,418.37 2,449,684.05 17,147,788.35
280 1 2005 1,352,577.13 2,449,684.05 17,147,788.35
281 4 2005 2,458,535.62 2,449,684.05 17,147,788.35
283 1 2005 1,573,012.94 2,449,684.05 17,147,788.35
284 1 2006 1,576,562.20 2,138,250.72 19,244,256.47
287 NULL 2006 519,905.93 2,138,250.72 19,244,256.47
285 NULL 2007 172,524.45 1,941,678.09 19,416,780.93
(10 row(s) affected)
See Also#
Excellent blog post about window functions and OVER, on sqlmag.com, by Itzik Ben-Gan