/*
 * Copyright 2004-2019 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.
 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. 
/**
 * A user-defined aggregate function needs to implement this interface.
 * The class must be public and must have a public non-argument constructor.
 * <p>
 * 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 {@link Aggregate} interface.
 * </p>
 */
public interface AggregateFunction {

    
This method is called when the aggregate function is used.
A new object is created for each invocation.
Params:
conn – a connection to the database/**
     * 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 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.
Params:
inputTypes – the SQL type of the parameters, Types
Returns:
the SQL type of the result/**
     * 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.
     *
     * @param inputTypes the SQL type of the parameters, {@link java.sql.Types}
     * @return the SQL type of the result
     */
    int getType(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.
Params:
value – the value(s) for this row/**
     * 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. 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/**
     * 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.
     *
     * @return the aggregated value
     */
    Object getResult() throws SQLException;

}