/*
* Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.api;
import java.sql.
Connection;
import java.sql.
SQLException;
/**
* A user-defined aggregate function needs to implement this interface.
* The class must be public and must have a public non-argument constructor.
*/
public interface
Aggregate {
/**
* This method is called when the aggregate function is used.
* A new object is created for each invocation.
*
* @param conn a connection to the database
*/
void
init(
Connection conn) throws
SQLException;
/**
* This method must return the H2 data type, {@link org.h2.value.Value},
* of the aggregate function, given the H2 data 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.
*
* @param inputTypes the H2 data type of the parameters,
* @return the H2 data type of the result
* @throws SQLException if the number/type of parameters passed is incorrect
*/
int
getInternalType(int[]
inputTypes) throws
SQLException;
/**
* This method is called once for each row.
* If the aggregate function is called with multiple parameters,
* those are passed as array.
*
* @param value the value(s) for this row
*/
void
add(
Object value) throws
SQLException;
/**
* This method returns the computed aggregate value.
*
* @return the aggregated value
*/
Object getResult() throws
SQLException;
}