15.00 - Window Aggregate Functions - Teradata Database

Teradata Database SQL Functions, Operators, Expressions, and Predicates

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Window Aggregate Functions

An aggregate function on which a window specification is applied is called a window aggregate function. Without a window specification, aggregate functions return one value for all qualified rows examined. Window aggregate functions return a new value for each of the qualifying rows participating in the query.

Thus, the following SELECT statement, which includes the aggregate AVG, returns one value only: the average of sales.

   SELECT AVG(sale) 
   FROM monthly_sales;

The AVG window function retains each qualifying row.

The following SELECT statement might return the results that follow.

   SELECT territory, smonth, sales,
   AVG(sales) OVER (PARTITION BY territory 
                    ORDER BY smonth ROWS 2 PRECEDING)
   FROM sales_history;
   territory  smonth   sales  Moving Avg(sales)
   ---------  -------  -----  -----------------
   East        199810     10                 10
   East        199811      4                  7
   East        199812     10                  8
   East        199901      7                  7
   East        199902     10                  9
   West        199810      8                  8
   West        199811     12                 10
   West        199812      7                  9
   West        199901     11                 10
   West        199902      6                  8

For ANSI SQL:2011 compliant aggregate functions to which a window specification can be applied, see Chapter 2: “Aggregate Functions.”

User-defined aggregate function to which a window specification can be applied, see “Window Aggregate UDF” on page 1330.