Class SqlSplittableAggFunction.CountSplitter

All Implemented Interfaces:
SqlSingletonAggFunction, SqlSplittableAggFunction
Enclosing interface:

public static class SqlSplittableAggFunction.CountSplitter extends 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(*).

  • Field Details

  • Constructor Details

    • CountSplitter

      public CountSplitter()
  • Method Details

    • split

      public AggregateCall split(AggregateCall aggregateCall, Mappings.TargetMapping mapping)
      Specified by:
      split in interface SqlSplittableAggFunction
    • other

      public @Nullable AggregateCall other(RelDataTypeFactory typeFactory, AggregateCall e)
      Description copied from interface: SqlSplittableAggFunction
      Called to generate an aggregate for the other side of the join than the side aggregate call's arguments come from. Returns null if no aggregate is required.
      Specified by:
      other in interface SqlSplittableAggFunction
    • 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
      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
      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
      • GROUPING(deptno) if 0 if deptno is being grouped, 1 otherwise

      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 SqlSingletonAggFunction
      rexBuilder - Rex builder
      inputRowType - Input row type
      aggregateCall - Aggregate call
      Expression for single row
    • merge

      public @Nullable 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
      top - top aggregate call
      bottom - bottom aggregate call
      Merged aggregate call, null if fails to merge aggregate calls