Ekspresi tabel umum (CTE)

Berlaku untuk: pemeriksaan Databricks SQL Databricks Runtime

Menentukan kumpulan hasil sementara yang mungkin dapat Anda referensikan beberapa kali dalam cakupan pernyataan SQL. CTE digunakan terutama dalam pernyataan SELECT .

Sintaks

WITH common_table_expression [, ...]

common_table_expression
  view_identifier [ ( column_identifier [, ...] ) ] [ AS ] ( query )

Parameter

• view_identifier

  Pengidentifikasi yang common_table_expression dapat dirujuk

• column_identifier

  Pengidentifikasi opsional tempat kolom common_table_expression dapat dirujuk.

  Jika column_identifiers ditentukan, jumlahnya harus cocok dengan jumlah kolom yang dikembalikan oleh query. Jika tidak ada nama yang ditentukan, nama kolom berasal dari query.

• Query

  Kueri yang menghasilkan tataan hasil.

Contoh

-- CTE with multiple column aliases
> WITH t(x, y) AS (SELECT 1, 2)
  SELECT * FROM t WHERE x = 1 AND y = 2;
   1   2

-- CTE in CTE definition
> WITH t AS (
    WITH t2 AS (SELECT 1)
    SELECT * FROM t2)
  SELECT * FROM t;
   1

-- CTE in subquery
> SELECT max(c) FROM (
    WITH t(c) AS (SELECT 1)
    SELECT * FROM t);
      1

-- CTE in subquery expression
> SELECT (WITH t AS (SELECT 1)
          SELECT * FROM t);
                1

-- CTE in CREATE VIEW statement
> CREATE VIEW v AS
    WITH t(a, b, c, d) AS (SELECT 1, 2, 3, 4)
    SELECT * FROM t;
> SELECT * FROM v;
   1   2   3   4

-- CTE names are scoped
> WITH t  AS (SELECT 1),
       t2 AS (
        WITH t AS (SELECT 2)
        SELECT * FROM t)
SELECT * FROM t2;
   2

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