SQL in a Nutshell, 2nd Edition

ANSI SQL Aggregate Functions

Aggregate functions return a single value based upon a set of other values. If used among other expressions in the item list of a SELECT statement, the SELECT must have a GROUP BY or HAVING clause. No GROUP BY or HAVING clause is required if the aggregate function is the only value retrieved by the SELECT statement. The supported aggregate functions and their syntax are listed in Table 4-1.

Table 4-1. ANSI SQL aggregate functions

Function	Usage
AVG(expression)	Computes the average value of a column given by expression.
CORR(dependent, independent)	Computes a correlation coefficient.
COUNT(expression)	Counts the rows defined by the expression.
COUNT(*)	Counts all rows in the specified table or view.
COVAR_POP ( dependent, independent)	Computes population covariance.
COVAR_SAMP( dependent, independent)	Computes sample covariance.
CUME_DIST( value_list) WITHIN GROUP (ORDER BY sort_list)	Computes the relative rank of a hypothetical row within a group of rows, where the rank is equal to the number of rows less than or equal to the hypothetical row divided by the number of rows in the group.
DENSE_RANK( value_list) WITHIN GROUP (ORDER BY sort_list)	Generates a dense rank (no ranks are skipped) for a hypothetical row (value_list) in a group of rows generated by GROUP BY.
MIN( expression)	Finds the minimum value in a column given by expression.
MAX( expression)	Finds the maximum value in a column given by expression.
PERCENT_RANK( value_list ...