AVG(expression)  the average (arithmetic mean) of all input values 
Finding the average value is available on the following data
types: smallint, integer,
bigint, real, double
precision, numeric, interval.
The result is of type numeric for any integer type
input, double precision for floatingpoint input,
otherwise the same as the input data type.

count(*)  number of input values  The return value is of type bigint. 
count(expression)  Counts the input values for which the value of expression is not NULL.
 The return value is of type bigint. 
max(expression)  the maximum value of expression across all input values  Available for all numeric, string, and date/time types. The
result has the same type as the input expression.

min(expression)  the minimum value of expression across all input values  Available for all numeric, string, and date/time types. The
result has the same type as the input expression.

stddev(expression)  the sample standard deviation of the input values 
Finding the standard deviation is available on the following
data types: smallint, integer,
bigint, real, double
precision, numeric. The result is of type
double precision for floatingpoint input,
otherwise numeric.

sum(expression)  sum of expression across all input values  Summation is available on the following data types:
smallint, integer,
bigint, real, double
precision, numeric, interval.
The result is of type bigint for smallint
or integer input, numeric for
bigint
input, double precision for floatingpoint input,
otherwise the same as the input data type.

variance(expression)  the sample variance of the input values 
The variance is the square of the standard deviation. The
supported data types and result types are the same as for
standard deviation.
