创建一个具有“with recursive"的递归视图.Teradata 中的声明

问题描述

我想通过以下可重现的示例在 Teradata 中创建递归视图(即 CREATE RECURSIVE VIEW):

I would like to create a recursive view in Teradata (i.e., CREATE RECURSIVE VIEW) from the following reproducible example:

CREATE VOLATILE TABLE vt1
(
    foo VARCHAR(10)
    , counter INTEGER
    , bar INTEGER
)
ON COMMIT PRESERVE ROWS;

INSERT INTO vt1 VALUES ('a', 1, '1');
INSERT INTO vt1 VALUES ('a', 2, '2');
INSERT INTO vt1 VALUES ('a', 3, '2');
INSERT INTO vt1 VALUES ('a', 4, '4');
INSERT INTO vt1 VALUES ('a', 5, '1');
INSERT INTO vt1 VALUES ('b', 1, '3');
INSERT INTO vt1 VALUES ('b', 2, '1');
INSERT INTO vt1 VALUES ('b', 3, '1');
INSERT INTO vt1 VALUES ('b', 4, '2');

WITH RECURSIVE cte (foo, counter, bar, rsum) AS
(
SELECT
    foo
  , counter
  , bar
  , bar AS rsum
FROM 
    vt1
QUALIFY ROW_NUMBER() OVER (PARTITION BY foo ORDER BY counter) = 1

UNION ALL

SELECT
    t.foo
  , t.counter
  , t.bar
  , CASE WHEN cte.rsum < 3 THEN t.bar + cte.rsum ELSE t.bar END
FROM
    vt1 t JOIN cte ON t.foo = cte.foo AND t.counter = cte.counter + 1
)

SELECT 
    cte.*
  , CASE WHEN rsum < 5 THEN 0 ELSE 1 END AS tester
FROM 
    cte
ORDER BY 
    foo
    , counter
;

这将创建此输出:

╔═════╦═════════╦═════╦══════╦════════╗
║ foo ║ counter ║ bar ║ rsum ║ tester ║
╠═════╬═════════╬═════╬══════╬════════╣
║ a   ║       1 ║   1 ║    1 ║      0 ║
║ a   ║       2 ║   2 ║    3 ║      0 ║
║ a   ║       3 ║   2 ║    5 ║      1 ║
║ a   ║       4 ║   4 ║    4 ║      0 ║
║ a   ║       5 ║   1 ║    5 ║      1 ║
║ b   ║       1 ║   3 ║    3 ║      0 ║
║ b   ║       2 ║   1 ║    4 ║      0 ║
║ b   ║       3 ║   1 ║    5 ║      1 ║
║ b   ║       4 ║   2 ║    2 ║      0 ║
╚═════╩═════════╩═════╩══════╩════════╝

我最终想保存"为一个视图.我已经尝试了 CREATE RECURSIVE VIEW 和几个变体，但我想我不明白如何绕过 WITH RECURSIVE cte 语句.

Which I would ultimately like to "save" as a view. I have tried CREATE RECURSIVE VIEW and several variants, but I think I'm not understanding how to get around the WITH RECURSIVE cte statement.

有关了解正在发生的事情的相关问题，请参阅此问题

For a related question to understand what's going on, see this question

推荐答案

好吧，这实际上比我想象的要难:

Okay, that was actually harder than I thought:

create recursive view db.test_view (
foo, counter,bar,rsum) as 
(SELECT
    foo,
    counter,
    bar,
    bar AS rsum
    FROM 
    vt1
    QUALIFY ROW_NUMBER() OVER (PARTITION BY foo ORDER BY counter) = 1

UNION ALL
SELECT
    t.foo,
    t.counter,
    t.bar,
    CASE WHEN cte.rsum < 5 THEN
        t.bar + cte.rsum
    ELSE t.bar 
    END
FROM
vt1 t
JOIN test_view cte
ON t.foo = cte.foo
AND t.counter = cte.counter + 1

)

不要限定递归连接到视图.IE，JOIN test_view，而不是 JOIN db.test_view.

Don't qualify the recursive join to the view. IE, JOIN test_view, not JOIN db.test_view.

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