SQL in a Nutshell, 3rd 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 aggregate functions supported by the ANSI SQL standard 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) WITHIN GROUP (ORDER BY sort_list ...