This topic describes the aggregate functions that are supported and unsupported by PolarDB-X.

Supported functions

The following table describes the aggregate functions that are supported by PolarDB-X.

Function Description
AVG(expression) Returns the average value of an expression. The expression is a field.
COUNT(expression) Returns the number of records in an expression. The expression is a field or an asterisk (*).
COUNT(DISTINCT expression) Returns the number of unique records in an expression.
MAX(expression) Returns the maximum value in an expression.
MIN(expression) Returns the minimum value in an expression.
SUM(expression) Returns the sum of all values in an expression.
BIT_OR(expression) Calculates the bitwise OR of an expression.
BIT_XOR(expression) Calculates the bitwise exclusive OR (XOR) of an expression.
BIT_AND(expression) Calculates the bitwise AND of an expression.
GROUP_CONCAT(expression)) Returns a concatenated string based on an expression.

Unsupported functions

The following table describes the aggregate functions that are not supported by PolarDB-X. These functions are supported by databases that run the MySQL 5.7 engine.

Function Description
STD() and STDDEV() Returns the standard deviation of an expression.
STDDEV_POP() Calculates the population standard deviation and returns the square root of the population variance.
STDDEV_SAMP() Calculates the cumulative sample standard deviation and returns the square root of the sample variance.