AggregateFunction (NanoDB SQL Relational Database 0.1-SNAPSHOT API)

java.lang.Object
- edu.caltech.nanodb.functions.Function
- - edu.caltech.nanodb.functions.ScalarFunction
  - - edu.caltech.nanodb.functions.AggregateFunction

All Implemented Interfaces:

java.lang.Cloneable

Direct Known Subclasses:

CountAggregate, CountStar, MinMaxAggregate, StdDevVarAggregate, SumAvgAggregate
```
public abstract class AggregateFunction
extends ScalarFunction
```
This class provides the general abstraction for aggregate functions.

Field Summary

Fields
Modifier and Type Field Description

private boolean supportsDistinct
If this flag is true, the aggregate function supports the DISTINCT keyword before its first argument.

Constructor Summary

Constructors
Constructor Description

AggregateFunction(boolean supportsDistinct)

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	Description
`abstract void`	`addValue(java.lang.Object value)`	Adds a value to the aggregate function so that it can update its internal state.
`abstract void`	`clearResult()`	Clears the aggregate function's current state so that the object can be reused to compute an aggregate on another set of input values.
`abstract java.lang.Object`	`getResult()`	Returns the aggregated result computed for this aggregate function.
`boolean`	`supportsDistinct()`

Methods inherited from class edu.caltech.nanodb.functions.ScalarFunction
getReturnType

Methods inherited from class edu.caltech.nanodb.functions.Function
clone

Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - supportsDistinct
```
private boolean supportsDistinct
```
    If this flag is true, the aggregate function supports the DISTINCT keyword before its first argument.
- Constructor Detail
  - AggregateFunction
```
public AggregateFunction(boolean supportsDistinct)
```
- Method Detail
  - supportsDistinct
```
public boolean supportsDistinct()
```
  - clearResult
```
public abstract void clearResult()
```
    Clears the aggregate function's current state so that the object can be reused to compute an aggregate on another set of input values.
  - addValue
```
public abstract void addValue(java.lang.Object value)
```
    Adds a value to the aggregate function so that it can update its internal state. Generally, aggregate functions ignore null inputs (which represent SQL NULL values) when computing their results.
    
    Parameters:
    
    value - the value to add to the aggregate function
  - getResult
```
public abstract java.lang.Object getResult()
```
    Returns the aggregated result computed for this aggregate function. Generally, if aggregate functions receive no non-null inputs then they should produce a null result. (COUNT is an exception to this rule, producing 0 in that case.)
    
    Returns:
    
    the result of the aggregate computation.