| 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 floating-point 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 floating-point 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 floating-point 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. |