org.h2.api

Interface AggregateFunction

public interface AggregateFunction

A user-defined aggregate function needs to implement this interface. The class must be public and must have a public non-argument constructor.

Please note this interface only has limited support for data types. If you need data types that don't have a corresponding SQL type (for example GEOMETRY), then use the Aggregate interface.

Method Summary

Modifier and Type	Method and Description
void	add(java.lang.Object value) This method is called once for each row.
java.lang.Object	getResult() This method returns the computed aggregate value.
int	getType(int[] inputTypes) This method must return the SQL type of the method, given the SQL type of the input data.
default void	init(java.sql.Connection conn) This method is called when the aggregate function is used.

Method Detail

init

default void init(java.sql.Connection conn)
           throws java.sql.SQLException

This method is called when the aggregate function is used. A new object is created for each invocation.

Parameters:

conn - a connection to the database

Throws:

java.sql.SQLException - on SQL exception

getType

int getType(int[] inputTypes)
     throws java.sql.SQLException

This method must return the SQL type of the method, given the SQL type of the input data. The method should check here if the number of parameters passed is correct, and if not it should throw an exception.

Parameters:

inputTypes - the SQL type of the parameters, Types

Returns:

the SQL type of the result

Throws:

java.sql.SQLException - on failure

add

void add(java.lang.Object value)
  throws java.sql.SQLException

This method is called once for each row. If the aggregate function is called with multiple parameters, those are passed as array.

Parameters:

value - the value(s) for this row

Throws:

java.sql.SQLException - on failure

getResult

java.lang.Object getResult()
                    throws java.sql.SQLException

This method returns the computed aggregate value. This method must preserve previously added values and must be able to reevaluate result if more values were added since its previous invocation.

Returns:

the aggregated value

Throws:

java.sql.SQLException - on failure