Class MaxMinAggregator
java.lang.Object
org.apache.derby.impl.sql.execute.SystemAggregator
org.apache.derby.impl.sql.execute.OrderableAggregator
org.apache.derby.impl.sql.execute.MaxMinAggregator
- All Implemented Interfaces:
Externalizable
,Serializable
,Formatable
,TypedFormat
,ExecAggregator
Aggregator for MAX()/MIN(). Defers most of its work
to OrderableAggregator.
- See Also:
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Field Summary
FieldsFields inherited from class org.apache.derby.impl.sql.execute.OrderableAggregator
value
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprotected void
accumulate
(DataValueDescriptor addend) Accumulateint
Get the formatID which corresponds to this class.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
void
setup
(ClassFactory cf, String aggregateName, DataTypeDescriptor returnType) Set's up the aggregate for processing.void
Although we are not expected to be persistent per se, we may be written out by the sorter temporarily.Methods inherited from class org.apache.derby.impl.sql.execute.OrderableAggregator
getResult, merge, toString
Methods inherited from class org.apache.derby.impl.sql.execute.SystemAggregator
accumulate, didEliminateNulls
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Field Details
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isMax
private boolean isMax
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Constructor Details
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MaxMinAggregator
public MaxMinAggregator()
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Method Details
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setup
Description copied from interface:ExecAggregator
Set's up the aggregate for processing.- Specified by:
setup
in interfaceExecAggregator
- Overrides:
setup
in classOrderableAggregator
- 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.
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accumulate
Accumulate- Specified by:
accumulate
in classSystemAggregator
- Parameters:
addend
- value to be added in- Throws:
StandardException
- on error
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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
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writeExternal
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 interfaceExternalizable
- Overrides:
writeExternal
in classOrderableAggregator
- Throws:
IOException
- on error- See Also:
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readExternal
- Specified by:
readExternal
in interfaceExternalizable
- Overrides:
readExternal
in classOrderableAggregator
- Throws:
IOException
- on errorClassNotFoundException
- on error- See Also:
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getTypeFormatId
public int getTypeFormatId()Get the formatID which corresponds to this class.- Returns:
- the formatID of this class
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