Aggregate functions are the function that is used to compute against a “returned column of numeric data” from your select statement. Aggregate functions basically summarize the results of a particular column of selected data. In aggregate function the values of multiple rows are grouped together as input on certain criteria to form a single value of more significant meaning or measurement such as a set, a bag or a list. All aggregate functions will ignore NULL values.
Most commonly used SQL aggregate functions are
MIN : Returns the smallest value in a given column.
MAX : Returns the largest value in a given column.
SUM : Returns the sum of the numeric values in a given column.
AVG : Returns the average value of a given column.
COUNT : Returns the total number of values in a given column.
COUNT(*) : Returns the number of rows in a table.
GROUPING : Is a column or an expression that contains a column in a GROUP BY clause.
STDEV : Returns the statistical standard deviation of all values in the specified expression.
STDEVP : Returns the statistical standard deviation for the population for all values in the specified expression.
VAR : Returns the statistical variance of all values in the specified expression, may be followed by the OVER clause.
VARP : Returns the statistical variance for the population for all values in the specified expression.
