Package nz.co.gregs.dbvolution.expressions

Class DurationExpression.FirstValueExpression

    • Constructor Detail

      • FirstValueExpression

        public FirstValueExpression()

    • Method Detail

      • toSQLString

        public String toSQLString​(DBDefinition db)
        Description copied from interface: HasSQLString
        Produces the snippet provided by this class.

        This is only used internally.

        If you are extending DBvolution and adding a new function this is the place to format the information for use in SQL. A DBDefinition instance is provided to supply context and so your SQL can used on multiple database engines.

        Specified by:
        toSQLString in interface HasSQLString
        Overrides:
        toSQLString in class AnyExpression<Duration,DurationResult,DBDuration>
        Parameters:
        db - the target database

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        Returns:
        the DBValue formatted as a SQL snippet

      • isAggregator

        public boolean isAggregator()
        Description copied from interface: DBExpression
        Returns TRUE if this expression is an Aggregator like SUM() or LEAST().

        Subclasses must implement this method returning TRUE if the expression will combine the results of several rows to produce a result. If the expression relies on subexpressions, then the isAggregator method must return TRUE if the subexpressions include an aggregator.

        Aggregators collect several rows together to produce a single result. Examples are MAX, MIN, and AVERAGE.

        They are only appropriate in the SELECT clause and generally require the GROUP BY clause to be useful.

        Aggregators are used with DBReport. Aggregator expressions are included in the SELECT clause but excluded from the GROUP BY clause.

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        Specified by:
        isAggregator in interface DBExpression
        Overrides:
        isAggregator in class AnyExpression<Duration,DurationResult,DBDuration>
        Returns:
        TRUE if this DBExpression represents an aggregating functions

      • copy

        public DurationExpression.FirstValueExpression copy()
        Description copied from interface: DBExpression
        A Complete Copy Of This DBValue.

        Immutability in DBvolution is maintain by internally copying objects.

        This method enables immutability by performing a deep copy of the object.

        Singletons may return themselves but all other objects must return a new instance with copies of all mutable fields.

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        Specified by:
        copy in interface DBExpression
        Specified by:
        copy in interface DurationResult
        Overrides:
        copy in class DurationExpression
        Returns:
        a copy of this DBValue

      • over

        public WindowFunctionFramable<DurationExpression> over()
        Description copied from interface: CanBeWindowingFunctionWithFrame
        Over creates a window function.

        Window functions allow access to data in the records right before and after the current record. A window function defines a frame or window of rows with a given length around the current row, and performs a calculation across the set of data in the window. Wikipedia has more information at https://en.wikipedia.org/wiki/SQL_window_function

        Specified by:
        over in interface CanBeWindowingFunctionWithFrame<DurationExpression>
        Returns:
        a windowing function start point