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Implement GROUP BY DISTINCT

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With grouping sets, it's possible that some of the grouping sets are
duplicate.  This is especially common with CUBE and ROLLUP clauses. For
example GROUP BY CUBE (a,b), CUBE (b,c) is equivalent to

  GROUP BY GROUPING SETS (
    (a, b, c),
    (a, b, c),
    (a, b, c),
    (a, b),
    (a, b),
    (a, b),
    (a),
    (a),
    (a),
    (c, a),
    (c, a),
    (c, a),
    (c),
    (b, c),
    (b),
    ()
  )

Some of the grouping sets are calculated multiple times, which is mostly
unnecessary.  This commit implements a new GROUP BY DISTINCT feature, as
defined in the SQL standard, which eliminates the duplicate sets.

Author: Vik Fearing
Reviewed-by: Erik Rijkers, Georgios Kokolatos, Tomas Vondra
Discussion: https://postgr.es/m/bf3805a8-d7d1-ae61-fece-761b7ff41ecc@postgresfriends.org
This commit is contained in:
Tomas Vondra
2021-03-18 17:45:38 +01:00
parent cd91de0d17
commit be45be9c33
18 changed files with 333 additions and 27 deletions
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2
src/backend/catalog/sql_features.txt
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@@ -482,7 +482,7 @@ T351 Bracketed SQL comments (/*...*/ comments) YES
T431 Extended grouping capabilities YES
T432 Nested and concatenated GROUPING SETS YES
T433 Multiargument GROUPING function YES
T434 GROUP BY DISTINCT NO
T434 GROUP BY DISTINCT YES
T441 ABS and MOD functions YES
T461 Symmetric BETWEEN predicate YES
T471 Result sets return value NO