org.apache.pig.builtin
Class COUNT_STAR

java.lang.Object
  org.apache.pig.EvalFunc<Long>
      org.apache.pig.builtin.COUNT_STAR

All Implemented Interfaces:

Accumulator<Long>, Algebraic

public class COUNT_STAR
extends EvalFunc<Long>
implements Algebraic, Accumulator<Long>

Generates the count of the values of the first field of a tuple. This class is different from COUNT in that it counts all NULL values and as such implements SQL COUNT(*) semantics. Generates the count of the number of values in a bag. This count does include null values, and thus matches SQL semantics for COUNT(*) (where in SQL indicates all) but not for COUNT(a) (where a is * field).

This class implements Algebraic, so if possible the execution will performed in a distributed fashion.

There are no restrictions as to the data types inside the bag to be counted.

COUNT_STAR implements the Accumulator interface as well. While this will never be the preferred method of usage it is available in case the combiner can not be used for a given calculation.

Nested Class Summary

static class	COUNT_STAR.Final
static class	COUNT_STAR.Initial
static class	COUNT_STAR.Intermediate

Field Summary

Fields inherited from class org.apache.pig.EvalFunc

log, pigLogger, reporter, returnType

Constructor Summary

COUNT_STAR()

Method Summary

void	accumulate(Tuple b) Pass tuples to the UDF.
void	cleanup() Called after getValue() to prepare processing for next key.
Long	exec(Tuple input) This callback method must be implemented by all subclasses.
String	getFinal() Get the final function.
String	getInitial() Get the initial function.
String	getIntermed() Get the intermediate function.
Long	getValue() Called when all tuples from current key have been passed to accumulate.
Schema	outputSchema(Schema input) Report the schema of the output of this UDF.
protected static Long	sum(Tuple input)

Methods inherited from class org.apache.pig.EvalFunc

finish, getArgToFuncMapping, getCacheFiles, getLogger, getPigLogger, getReporter, getReturnType, getSchemaName, isAsynchronous, progress, setPigLogger, setReporter, warn

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

COUNT_STAR

public COUNT_STAR()

Method Detail

exec

public Long exec(Tuple input)
          throws IOException

Description copied from class: EvalFunc

This callback method must be implemented by all subclasses. This is the method that will be invoked on every Tuple of a given dataset. Since the dataset may be divided up in a variety of ways the programmer should not make assumptions about state that is maintained between invocations of this method.

Specified by:

exec in class EvalFunc<Long>

Parameters:

input - the Tuple to be processed.

Returns:

result, of type T.

Throws:

IOException

getInitial

public String getInitial()

Description copied from interface: Algebraic

Get the initial function.

Specified by:

getInitial in interface Algebraic

Returns:

A function name of f_init. f_init should be an eval func.

getIntermed

public String getIntermed()

Description copied from interface: Algebraic

Get the intermediate function.

Specified by:

getIntermed in interface Algebraic

Returns:

A function name of f_intermed. f_intermed should be an eval func.

getFinal

public String getFinal()

Description copied from interface: Algebraic

Get the final function.

Specified by:

getFinal in interface Algebraic

Returns:

A function name of f_final. f_final should be an eval func parametrized by the same datum as the eval func implementing this interface.

sum

protected static Long sum(Tuple input)
                   throws ExecException,
                          NumberFormatException

Throws:

ExecException

NumberFormatException

outputSchema

public Schema outputSchema(Schema input)

Description copied from class: EvalFunc

Report the schema of the output of this UDF. Pig will make use of this in error checking, optimization, and planning. The schema of input data to this UDF is provided.

Overrides:

outputSchema in class EvalFunc<Long>

Parameters:

input - Schema of the input

Returns:

Schema of the output

accumulate

public void accumulate(Tuple b)
                throws IOException

Description copied from interface: Accumulator

Pass tuples to the UDF.

Specified by:

accumulate in interface Accumulator<Long>

Parameters:

b - A tuple containing a single field, which is a bag. The bag will contain the set of tuples being passed to the UDF in this iteration.

Throws:

IOException

cleanup

public void cleanup()

Description copied from interface: Accumulator

Called after getValue() to prepare processing for next key.

Specified by:

cleanup in interface Accumulator<Long>

getValue

public Long getValue()

Description copied from interface: Accumulator

Called when all tuples from current key have been passed to accumulate.

Specified by:

getValue in interface Accumulator<Long>

Returns:

the value for the UDF for this key.