/*
* Copyright 2004-2023 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://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
* @throws SQLException on SQL exception
*/
default void init(Connection conn) throws SQLException {
// Do nothing by default
}
/**
* 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
* @throws SQLException on failure
*/
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.
*
* @return the aggregated value
* @throws SQLException on failure
*/
Object getResult() throws SQLException;
}