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Oracle® Database SQL Language Reference
12c Release 1 (12.1)

E17209-15
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Aggregate Functions

Aggregate functions return a single result row based on groups of rows, rather than on single rows. Aggregate functions can appear in select lists and in ORDER BY and HAVING clauses. They are commonly used with the GROUP BY clause in a SELECT statement, where Oracle Database divides the rows of a queried table or view into groups. In a query containing a GROUP BY clause, the elements of the select list can be aggregate functions, GROUP BY expressions, constants, or expressions involving one of these. Oracle applies the aggregate functions to each group of rows and returns a single result row for each group.

If you omit the GROUP BY clause, then Oracle applies aggregate functions in the select list to all the rows in the queried table or view. You use aggregate functions in the HAVING clause to eliminate groups from the output based on the results of the aggregate functions, rather than on the values of the individual rows of the queried table or view.

See Also:

"Using the GROUP BY Clause: Examples" and the "HAVING Clause" for more information on the GROUP BY clause and HAVING clauses in queries and subqueries

Many (but not all) aggregate functions that take a single argument accept these clauses:

For example, the DISTINCT average of 1, 1, 1, and 3 is 2. The ALL average is 1.5. If you specify neither, then the default is ALL.

Some aggregate functions allow the windowing_clause, which is part of the syntax of analytic functions. Refer to windowing_clause for information about this clause. In the listing of aggregate functions at the end of this section, the functions that allow the windowing_clause are followed by an asterisk (*)

All aggregate functions except COUNT(*), GROUPING, and GROUPING_ID ignore nulls. You can use the NVL function in the argument to an aggregate function to substitute a value for a null. COUNT and REGR_COUNT never return null, but return either a number or zero. For all the remaining aggregate functions, if the data set contains no rows, or contains only rows with nulls as arguments to the aggregate function, then the function returns null.

The aggregate functions MIN, MAX, SUM, AVG, COUNT, VARIANCE, and STDDEV, when followed by the KEEP keyword, can be used in conjunction with the FIRST or LAST function to operate on a set of values from a set of rows that rank as the FIRST or LAST with respect to a given sorting specification. Refer to FIRST for more information.

You can nest aggregate functions. For example, the following example calculates the average of the maximum salaries of all the departments in the sample schema hr:

SELECT AVG(MAX(salary))
  FROM employees
  GROUP BY department_id;

AVG(MAX(SALARY))
----------------
      10926.3333

This calculation evaluates the inner aggregate (MAX(salary)) for each group defined by the GROUP BY clause (department_id), and aggregates the results again.

In the list of aggregate functions that follows, functions followed by an asterisk (*) allow the windowing_clause.


AVG
COLLECT
CORR
CORR_*
COUNT
COVAR_POP
COVAR_SAMP
CUME_DIST
DENSE_RANK
FIRST
GROUP_ID
GROUPING
GROUPING_ID
LAST
LISTAGG
MAX
MEDIAN
MIN
PERCENT_RANK
PERCENTILE_CONT
PERCENTILE_DISC
RANK
REGR_ (Linear Regression) Functions
STATS_BINOMIAL_TEST
STATS_CROSSTAB
STATS_F_TEST
STATS_KS_TEST
STATS_MODE
STATS_MW_TEST
STATS_ONE_WAY_ANOVA
STATS_T_TEST_*
STATS_WSR_TEST
STDDEV
STDDEV_POP
STDDEV_SAMP
SUM
SYS_XMLAGG
VAR_POP
VAR_SAMP
VARIANCE
XMLAGG