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  1. MariaDB Server
  2. MDEV-39725

CREATE VIEW extraction changes row multiplicity for DISTINCT over grouped aggregate results

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    Description

      Under semantic-equivalent rewriting, extracting a grouped aggregate into a view causes a stable row-count mismatch on MariaDB.
      The source and mutated queries are logically equivalent, but produce different results.

      CREATE TABLE t1 (c4 INT NULL);
      		 
      INSERT INTO t1 (c4) VALUES (1);
      		 
      INSERT INTO t1 (c4) VALUES (2);
      		 
       
      		 
      -- Source Original SQL
      		 
      SELECT DISTINCT VARIANCE(fqd39.c4) AS col_2 FROM t1 AS fqd39 GROUP BY fqd39.c4;
      		 
       
      		 
      -- View SQL
      		 
      CREATE VIEW v AS SELECT VARIANCE(fqd39.c4) AS col_2 FROM t1 AS fqd39 GROUP BY fqd39.c4;
      		 
       
      		 
      -- Mutated SQL
      		 
      SELECT DISTINCT v.col_2 AS col_2 FROM v;

      Observed result - Query A (original):

      col_2
      0.0
      0.0

      Observed result - Query B (mutated):

      col_2
      0.0

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          is duplicated by

          Bug - A problem which impairs or prevents the functions of the product. MDEV-39726 CREATE VIEW extraction changes COUNT(*) result for ordered grouped VAR_SAMP(... ) IS NULL query

          • Major - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-39734 Replacing a base table with an equivalent passthrough view makes a valid grouped expression query fail under `ONLY_FULL_GROUP_BY`

          • Major - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-39737 CREATE VIEW with `ALGORITHM=MERGE` and `ALGORITHM=TEMPTABLE` return different grouped `VAR_SAMP(...)` results under `HAVING ... IS NULL`

          • Major - Major loss of function.
          • Closed

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              psergei Sergei Petrunia
              pyuan Peiyuan Liu
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              Dates

                Created:
                Updated:

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