Class SqlSplittableAggFunction.CountSplitter

  • All Implemented Interfaces:
    SqlSplittableAggFunction
    Enclosing interface:
    SqlSplittableAggFunction

    public static class SqlSplittableAggFunction.CountSplitter
    extends java.lang.Object
    implements SqlSplittableAggFunction
    Splitting strategy for COUNT.

    COUNT splits into itself followed by SUM. (Actually SUM0, because the total needs to be 0, not null, if there are 0 rows.) This rule works for any number of arguments to COUNT, including COUNT(*).

    • Constructor Detail

      • CountSplitter

        public CountSplitter()
    • Method Detail

      • topSplit

        public AggregateCall topSplit​(RexBuilder rexBuilder,
                                      SqlSplittableAggFunction.Registry<RexNode> extra,
                                      int offset,
                                      RelDataType inputRowType,
                                      AggregateCall aggregateCall,
                                      int leftSubTotal,
                                      int rightSubTotal)
        Description copied from interface: SqlSplittableAggFunction
        Generates an aggregate call to merge sub-totals.

        Most implementations will add a single aggregate call to aggCalls, and return a RexInputRef that points to it.

        Specified by:
        topSplit in interface SqlSplittableAggFunction
        Parameters:
        rexBuilder - Rex builder
        extra - Place to define extra input expressions
        offset - Offset due to grouping columns (and indicator columns if applicable)
        inputRowType - Input row type
        aggregateCall - Source aggregate call
        leftSubTotal - Ordinal of the sub-total coming from the left side of the join, or -1 if there is no such sub-total
        rightSubTotal - Ordinal of the sub-total coming from the right side of the join, or -1 if there is no such sub-total
        Returns:
        Aggregate call
      • singleton

        public RexNode singleton​(RexBuilder rexBuilder,
                                 RelDataType inputRowType,
                                 AggregateCall aggregateCall)
        Generates an expression for the value of the aggregate function when applied to a single row.

        For example, if there is one row:

        • SUM(x) is x
        • MIN(x) is x
        • MAX(x) is x
        • COUNT(x) is CASE WHEN x IS NOT NULL THEN 1 ELSE 0 END 1 which can be simplified to 1 if x is never null
        • COUNT(*) is 1

        COUNT(*), and COUNT applied to all NOT NULL arguments, become 1; otherwise CASE WHEN arg0 IS NOT NULL THEN 1 ELSE 0 END.

        Specified by:
        singleton in interface SqlSplittableAggFunction
        Parameters:
        rexBuilder - Rex builder
        inputRowType - Input row type
        aggregateCall - Aggregate call
        Returns:
        Expression for single row
      • merge

        public AggregateCall merge​(AggregateCall top,
                                   AggregateCall bottom)
        Description copied from interface: SqlSplittableAggFunction
        Merge top and bottom aggregate calls into a single aggregate call, if they are legit to merge.

        SUM of SUM becomes SUM; SUM of COUNT becomes COUNT; MAX of MAX becomes MAX; MIN of MIN becomes MIN. AVG of AVG would not match, nor would COUNT of COUNT.

        Specified by:
        merge in interface SqlSplittableAggFunction
        Parameters:
        top - top aggregate call
        bottom - bottom aggregate call
        Returns:
        Merged aggregate call, null if fails to merge aggregate calls