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Cláusula DISTRIBUTE BY

  • Artigo

Aplica-se a: marca de seleção positiva SQL do Databricks marca de seleção positiva Runtime do Databricks

Reparticiona os dados com base nas expressões de entrada. Ao contrário da cláusula CLUSTER BY, não classifica os dados em cada partição.

Sintaxe

DISTRIBUTE BY expression [, ...]

Parâmetros

Exemplos

> CREATE TEMP VIEW person (name, age)
  AS VALUES ('Zen Hui', 25),
            ('Anil B', 18),
            ('Shone S', 16),
            ('Mike A', 25),
            ('John A', 18),
            ('Jack N', 16);

-- Reduce the number of shuffle partitions to 2 to illustrate the behavior of `DISTRIBUTE BY`.
-- It's easier to see the clustering and sorting behavior with less number of partitions.
> SET spark.sql.shuffle.partitions = 2;

-- Select the rows with no ordering. Please note that without any sort directive, the result
-- of the query is not deterministic. It's included here to just contrast it with the
-- behavior of `DISTRIBUTE BY`. The query below produces rows where age columns are not
-- clustered together.
> SELECT age, name FROM person;
  16 Shone S
  25 Zen Hui
  16  Jack N
  25  Mike A
  18  John A
  18  Anil B

-- Produces rows clustered by age. Persons with same age are clustered together.
-- Unlike `CLUSTER BY` clause, the rows are not sorted within a partition.
> SELECT age, name FROM person DISTRIBUTE BY age;
  25 Zen Hui
  25  Mike A
  18  John A
  18  Anil B
  16 Shone S
  16  Jack N