通用 table 表示式 （CTE）

適用於：Databricks SQL Databricks Runtime

定義一個暫時的結果 set，您可以在 SQL 語句的範圍內多次引用。 CTE 主要用於 SELECT 語句。

語法

WITH common_table_expression [, ...]

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

Parameters

• view_identifier

  能用來參考 common_table_expression 的 identifier

• column_identifier

  可選的 identifier，可用於參考 common_table_expression 中的 column。

  如果指定了 column_identifier，則其數目必須符合 query所傳回的 columns 數目。 如果未指定名稱，則 column 名稱衍生自 query。

• query

  產生結果的查詢 set。

範例

-- 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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