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公用表表达式 (CTE)

  • 项目

适用于：勾选“是” Databricks SQL 勾选“是” Databricks Runtime

定义一个可在 SQL 语句的范围内多次引用的临时结果集。 CTE 主要在 SELECT 语句中使用。

语法

WITH common_table_expression [, ...]

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

参数

  • view_identifier

    可按其引用 common_table_expression 的标识符

  • column_identifier

    可按其引用 common_table_expression 的列的可选标识符。

    如果指定了 column_identifier，则其数量必须与 query 返回的列数相匹配。 如果未指定任何名称，则列名称派生自 query。

  • query

    生成结果集的查询。

示例

-- 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