CountAggregator (Apache Derby V10.14 Internals)

java.lang.Object
- org.apache.derby.impl.sql.execute.SystemAggregator
- - org.apache.derby.impl.sql.execute.CountAggregator

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, Formatable, TypedFormat, ExecAggregator
```
public final class CountAggregator
extends SystemAggregator
```
Aggregator for COUNT()/COUNT(*).

See Also:

Serialized Form

Field Summary

Fields
Modifier and Type Field Description

private boolean isCountStar

private long value

Fields
Modifier and Type	Field	Description
`private boolean`	`isCountStar`
`private long`	`value`

Constructor Summary

Constructors
Constructor Description

CountAggregator()

Constructors
Constructor	Description
`CountAggregator()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`protected void`	`accumulate(DataValueDescriptor addend)`
`void`	`accumulate(DataValueDescriptor addend, java.lang.Object ga)`	Accumulate for count().
`DataValueDescriptor`	`getResult()`	Return the result of the aggregation.
`int`	`getTypeFormatId()`	Get the formatID which corresponds to this class.
`boolean`	`isCountStar()`
`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`	`setup(ClassFactory cf, java.lang.String aggregateName, DataTypeDescriptor returnType)`	Set's up the aggregate for processing.
`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.SystemAggregator
didEliminateNulls, toString

- Field Detail
  - value
```
private long value
```
  - isCountStar
```
private boolean isCountStar
```
- Constructor Detail
  - CountAggregator
```
public CountAggregator()
```
- Method Detail
  - setup
```
public void setup(ClassFactory cf,
                  java.lang.String aggregateName,
                  DataTypeDescriptor returnType)
```
    Description copied from interface: ExecAggregator
    
    Set's up the aggregate for processing.
    
    Parameters:
    
    cf - Database-specific class factory.
    
    aggregateName - For builtin aggregates, this is a SQL aggregate name like MAX. For user-defined aggregates, this is the name of the user-written class which implements org.apache.derby.agg.Aggregator.
    
    returnType - The type returned by the getResult() method.
  - 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();
                } 
```
    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()
```
    Return the result of the aggregation. Just spit out the running count.
    
    Returns:
    
    the value as a Long
  - accumulate
```
public void accumulate(DataValueDescriptor addend,
                       java.lang.Object ga)
                throws StandardException
```
    Accumulate for count(). Toss out all nulls in this kind of count. Increment the count for count(*). Count even the null values.
    
    Specified by:
    
    accumulate in interface ExecAggregator
    
    Overrides:
    
    accumulate in class SystemAggregator
    
    Parameters:
    
    addend - value to be added in
    
    ga - the generic aggregator that is calling me
    
    Throws:
    
    StandardException - on error
    
    See Also:
    
    ExecAggregator.accumulate(org.apache.derby.iapi.types.DataValueDescriptor, java.lang.Object)
  - accumulate
```
protected final void accumulate(DataValueDescriptor addend)
```
    Specified by:
    
    accumulate in class SystemAggregator
  - 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.
    
    Returns:
    
    ExecAggregator the new aggregator
  - isCountStar
```
public boolean isCountStar()
```
  - writeExternal
```
public final void writeExternal(java.io.ObjectOutput out)
                         throws java.io.IOException
```
    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.
    
    Specified by:
    
    writeExternal in interface java.io.Externalizable
    
    Overrides:
    
    writeExternal in class SystemAggregator
    
    Throws:
    
    java.io.IOException - thrown on error
  - readExternal
```
public final 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 SystemAggregator
    
    Throws:
    
    java.io.IOException - io exception
    
    java.lang.ClassNotFoundException - on error
    
    See Also:
    
    Externalizable.readExternal(java.io.ObjectInput)
  - getTypeFormatId
```
public int getTypeFormatId()
```
    Get the formatID which corresponds to this class.
    
    Returns:
    
    the formatID of this class

Class CountAggregator

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

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

Field Detail

value

isCountStar

Constructor Detail

CountAggregator

Method Detail

setup

merge

getResult

accumulate

accumulate

newAggregator

isCountStar

writeExternal

readExternal

getTypeFormatId