## 12.20 Aggregate Functions

[12.20.1 Aggregate Function Descriptions](aggregate-functions.html)
[12.20.2 GROUP BY Modifiers](group-by-modifiers.html)
[12.20.3 MySQL Handling of GROUP BY](group-by-handling.html)
[12.20.4 Detection of Functional Dependence](group-by-functional-dependence.html)

 Aggregate functions operate on sets of values. They are often used with a `GROUP BY` clause to group values into subsets. This section describes most aggregate functions. For information about aggregate functions that operate on geometry values, see [Section 12.17.12, “Spatial Aggregate Functions”](spatial-aggregate-functions.html).

