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. |

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. |