Package dev.frostlake.functions.aggregate

Class HashAgg

java.lang.Object
dev.frostlake.functions.BuiltInFunction
dev.frostlake.functions.AggregateFunction
dev.frostlake.functions.aggregate.HashAgg
public class HashAgg extends AggregateFunction
HASH_AGG(expr) — a single, order-INDEPENDENT signed 64-bit hash over the whole (multi)set of input rows. Each row is hashed with the same FNV-1a used by the scalar HASH() function and the per-row hashes are combined commutatively (summed), so the result depends only on the multiset of values, not the row order.

Like HASH(), this does NOT reproduce Snowflake's proprietary HASH_AGG values — rely on its stability within this engine only. The RELATIONS are live-verified: the order of rows and of partial merges is immaterial, duplicates each contribute, a number's scale is invisible, the ARGUMENT order matters, DISTINCT drops repeats, an empty group is 0 while a group of NULLs is not — and a group of ONE row does not equal the scalar HASH of that row.

  • Constructor Details

    • HashAgg

      public HashAgg()

  • Method Details

    • createAccumulator

      public AggregateFunction.Accumulator createAccumulator()
      Description copied from class: AggregateFunction
      Creates the fresh, empty per-group state for one evaluation of this aggregate; the executor makes one per group (or per window partition) and never shares them.
      Specified by:
      createAccumulator in class AggregateFunction
      Returns:
      a new accumulator starting from this aggregate's empty-group state

    • geoRejection

      public SemiStructuredRejection geoRejection(int position)
      A GEOSPATIAL value is not hashable here, where an OBJECT is. Live, HASH_AGG(o) over a populated OBJECT column returns a number while HASH_AGG(g) over a GEOGRAPHY is "Invalid argument types for function 'HASH_AGG': (GEOGRAPHY)" (SQLSTATE 42P13) — so the inherited default, which reads the two semi-structured answers and finds neither, would be wrong. The SCALAR HASH(g) is deliberately untouched: it ACCEPTS a geo value live and returned one hash per row.
      Overrides:
      geoRejection in class BuiltInFunction
      Parameters:
      position - the zero-based argument position being asked about
      Returns:
      the refusal this position gives a GEOGRAPHY or GEOMETRY value; by default, the union of the two semi-structured answers

    • evaluate

      public Object evaluate(List<Object> args)
      Description copied from class: BuiltInFunction
      Computes the function's result over its already-evaluated argument values. A SQL NULL argument arrives as Java null, and returning null makes the SQL result NULL.
      Specified by:
      evaluate in class BuiltInFunction
      Parameters:
      args - the argument values, in call order
      Returns:
      the function's value for these arguments, or null for SQL NULL

    • getMinArgCount

      public int getMinArgCount()
      Description copied from class: BuiltInFunction
      The fewest arguments a call to this function may pass; fewer is an argument-count error.
      Specified by:
      getMinArgCount in class BuiltInFunction
      Returns:
      the minimum accepted argument count

    • getMaxArgCount

      public int getMaxArgCount()
      Live folds as many arguments as are written, exactly as the scalar HASH does.
      Specified by:
      getMaxArgCount in class BuiltInFunction
      Returns:
      the maximum accepted argument count