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

      All Methods Instance Methods Abstract Methods Default Methods 
      Modifier and Type Method 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