在PostgreSQL中使用REC里面的WITH

Question

在PostgreSQL中,另一个WITH可以使用WITH,例如:

WITH num AS (
    VALUES (50)
), num2 AS (
    SELECT column1 * 2 AS value FROM num
)
SELECT value FROM num2;

还有RECURSIVE WITHs,可以这样做:

WITH RECURSIVE t(n) AS (
    VALUES (1)
  UNION ALL
    SELECT n+1 FROM t WHERE n < 100
)
SELECT sum(n) FROM t;

但到目前为止,我还没有找到一种方法让RECURSIVE WITH使用之前的WITH.我认为它应该是这样的:

WITH num AS (
    VALUES (50)
), num2 AS (
    SELECT column1 * 2 AS value FROM num
), RECURSIVE  t(n) AS (
        VALUES (1)
    UNION ALL
        SELECT n+1 FROM t WHERE n < (SELECT * FROM num2)
)
SELECT sum(n) FROM t;

但这不起作用.有没有办法做到这一点？如果是这样,怎么样？

Answer 1

从开始WITH RECURSIVE.您仍然可以在递归部分之前挤入"常规"CTE:

WITH RECURSIVE
   num  AS (VALUES (50))
,  num2 AS (SELECT column1 * 2 AS value FROM num)
,  t(n) AS (
      VALUES (1)
      UNION ALL
      SELECT n+1 FROM t WHERE n < (SELECT * FROM num2)
   )
SELECT sum(n) FROM t;

- > SQLfiddle演示.