| Interface | Description | 
|---|---|
| AggregateFunc | Base class of the Aggregate Functions. | 
| Class | Description | 
|---|---|
| Aggregation | Aggregation in SQL statement. | 
| Avg | An aggregate function that returns the mean of all the values in a group. | 
| Count | An aggregate function that returns the number of the specific row in a group. | 
| CountStar | An aggregate function that returns the number of rows in a group. | 
| GeneralAggregateFunc | The general implementation of  AggregateFunc, which contains the upper-cased function
 name, the `isDistinct` flag and all the inputs. | 
| Max | An aggregate function that returns the maximum value in a group. | 
| Min | An aggregate function that returns the minimum value in a group. | 
| Sum | An aggregate function that returns the summation of all the values in a group. | 
| UserDefinedAggregateFunc | The general representation of user defined aggregate function, which implements
  AggregateFunc, contains the upper-cased function name, the canonical function name,
 the `isDistinct` flag and all the inputs. |