Aggregate Functions

COUNT() 

Returns the number of rows that matches a specified criterion.

count(*) - Returns the number of records in a table.

count(expression) - Returns number of rows where expression is not NULL.

count(distinct expression) - Returns number of distinct values of expression.

AVG()
avg(expression) - Average (arithmetic) of expression.

MIN()
min(expression) - Minimum value for expression.

MAX()
max(expression) - Maximum value for expression.

SUM()
sum(expression) - Sum of the values of expression.

STDDEV_POP()
stddev_pop(expression) - Population standard deviation.

STDDEV_SAMP()
stddev_samp(expression) - Unbiased sample standard deviation.

VAR_POP()
var_pop(expression) - Population variance.

VAR_SAMP()
var_samp(expression) - Unbiased sample variance.