AvgAggregator (Apache Derby V10.14 Internals)

java.lang.Object
- org.apache.derby.impl.sql.execute.SystemAggregator
- - org.apache.derby.impl.sql.execute.OrderableAggregator
  - - org.apache.derby.impl.sql.execute.SumAggregator
    - - org.apache.derby.impl.sql.execute.AvgAggregator

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, Formatable, TypedFormat, ExecAggregator
```
public final class AvgAggregator
extends SumAggregator
```
Aggregator for AVG(). Extends the SumAggregator and implements a count. Result is then sum()/count(). To handle overflow we catch the exception for value out of range, then we swap the holder for the current sum to one that can handle a larger range. Eventually a sum may end up in a SQLDecimal which can handle an infinite range. Once this type promotion has happened, it will not revert back to the original type, even if the sum would fit in a lesser type.

See Also:

Serialized Form

Field Summary

Fields
Modifier and Type Field Description

private long count

private int scale
- Fields inherited from class org.apache.derby.impl.sql.execute.OrderableAggregator
  value

Fields
Modifier and Type	Field	Description
`private long`	`count`
`private int`	`scale`

Constructor Summary

Constructors
Constructor Description

AvgAggregator()

Constructors
Constructor	Description
`AvgAggregator()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`protected void`	`accumulate(DataValueDescriptor addend)`	Accumulate
`DataValueDescriptor`	`getResult()`	Return the result of the aggregation.
`int`	`getTypeFormatId()`	Get the formatID which corresponds to this class.
`void`	`merge(ExecAggregator addend)`	Merges one aggregator into a another aggregator.
`ExecAggregator`	`newAggregator()`	Return a new initialized copy of this aggregator, any state set by the setup() method of the original Aggregator must be copied into the new aggregator.
`void`	`readExternal(java.io.ObjectInput in)`
`void`	`writeExternal(java.io.ObjectOutput out)`	Although we are not expected to be persistent per se, we may be written out by the sorter temporarily.

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

Methods inherited from class org.apache.derby.impl.sql.execute.OrderableAggregator
setup

Methods inherited from class org.apache.derby.impl.sql.execute.SumAggregator
toString

Methods inherited from class org.apache.derby.impl.sql.execute.SystemAggregator
accumulate, didEliminateNulls

- Field Detail
  - count
```
private long count
```
  - scale
```
private int scale
```
- Constructor Detail
  - AvgAggregator
```
public AvgAggregator()
```
- Method Detail
  - accumulate
```
protected void accumulate(DataValueDescriptor addend)
                   throws StandardException
```
    Description copied from class: SumAggregator
    
    Accumulate
    
    Overrides:
    
    accumulate in class SumAggregator
    
    Parameters:
    
    addend - value to be added in
    
    Throws:
    
    StandardException - on error
    
    See Also:
    
    ExecAggregator.accumulate(org.apache.derby.iapi.types.DataValueDescriptor, java.lang.Object)
  - merge
```
public void merge(ExecAggregator addend)
           throws StandardException
```
    Description copied from interface: ExecAggregator
    Merges one aggregator into a another aggregator. Merges two partial aggregates results into a single result. Needed for:
    - parallel aggregation
    - vector aggregation (GROUP BY)
    - distinct aggregates (e.g. MAX(DISTINCT Col))
    An example of a merge would be: given two COUNT() aggregators, C1 and C2, a merge of C1 into C2 would set C1.count += C2.count. So, given a CountAggregator with a getCount() method that returns its counts, its merge method might look like this:
```
                public void merge(ExecAggregator inputAggregator) throws StandardException
                {
                   count += ((CountAccgregator)inputAggregator).getCount();
                } 
```
    Specified by:
    
    merge in interface ExecAggregator
    
    Overrides:
    
    merge in class OrderableAggregator
    
    Parameters:
    
    addend - the other Aggregator (input partial aggregate)
    
    Throws:
    
    StandardException - on error
    
    See Also:
    
    ExecAggregator.merge(org.apache.derby.iapi.sql.execute.ExecAggregator)
  - getResult
```
public DataValueDescriptor getResult()
                              throws StandardException
```
    Return the result of the aggregation. If the count is zero, then we haven't averaged anything yet, so we return null. Otherwise, return the running average as a double.
    
    Specified by:
    
    getResult in interface ExecAggregator
    
    Overrides:
    
    getResult in class OrderableAggregator
    
    Returns:
    
    null or the average as Double
    
    Throws:
    
    StandardException - on error
  - newAggregator
```
public ExecAggregator newAggregator()
```
    Description copied from interface: ExecAggregator
    
    Return a new initialized copy of this aggregator, any state set by the setup() method of the original Aggregator must be copied into the new aggregator.
    
    Specified by:
    
    newAggregator in interface ExecAggregator
    
    Overrides:
    
    newAggregator in class SumAggregator
    
    Returns:
    
    ExecAggregator the new aggregator
  - writeExternal
```
public void writeExternal(java.io.ObjectOutput out)
                   throws java.io.IOException
```
    Description copied from class: OrderableAggregator
    
    Although we are not expected to be persistent per se, we may be written out by the sorter temporarily. So we need to be able to write ourselves out and read ourselves back in. We rely on formatable to handle situations where value is null.
    Why would we be called to write ourselves out if we are null? For scalar aggregates, we don't bother setting up the aggregator since we only need a single row. So for a scalar aggregate that needs to go to disk, the aggregator might be null.
    
    Specified by:
    
    writeExternal in interface java.io.Externalizable
    
    Overrides:
    
    writeExternal in class OrderableAggregator
    
    Throws:
    
    java.io.IOException - on error
    
    See Also:
    
    Externalizable.writeExternal(java.io.ObjectOutput)
  - readExternal
```
public void readExternal(java.io.ObjectInput in)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException
```
    Specified by:
    
    readExternal in interface java.io.Externalizable
    
    Overrides:
    
    readExternal in class OrderableAggregator
    
    Throws:
    
    java.io.IOException - on error
    
    java.lang.ClassNotFoundException - on error
    
    See Also:
    
    Externalizable.readExternal(java.io.ObjectInput)
  - getTypeFormatId
```
public int getTypeFormatId()
```
    Get the formatID which corresponds to this class.
    
    Specified by:
    
    getTypeFormatId in interface TypedFormat
    
    Overrides:
    
    getTypeFormatId in class SumAggregator
    
    Returns:
    
    the formatID of this class

Class AvgAggregator

Field Summary

Fields inherited from class org.apache.derby.impl.sql.execute.OrderableAggregator

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from class org.apache.derby.impl.sql.execute.OrderableAggregator

Methods inherited from class org.apache.derby.impl.sql.execute.SumAggregator

Methods inherited from class org.apache.derby.impl.sql.execute.SystemAggregator

Field Detail

count

scale

Constructor Detail

AvgAggregator

Method Detail

accumulate

merge

getResult

newAggregator

writeExternal

readExternal

getTypeFormatId