Package 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
    Description
    void
    add(Object value)
    This method is called once for each row.
    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(Connection conn)
    This method is called when the aggregate function is used.

  • Method Details

    • init

      default void init(Connection conn) throws 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:
      SQLException - on SQL exception

    • getType

      int getType(int[] inputTypes) 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.
      Parameters:
      inputTypes - the SQL type of the parameters, Types
      Returns:
      the SQL type of the result
      Throws:
      SQLException - on failure

    • add

      void add(Object value) throws 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:
      SQLException - on failure

    • getResult

      Object getResult() 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
      Throws:
      SQLException - on failure