从递归查询中删除行

Question

当我在我的数据库中运行这个查询时，我得到以下信息：

WITH RECURSIVE series AS (
    SELECT CONCAT( a.title) as str, a.prequelID
    FROM ( Prequels NATURAL JOIN Books) AS a
    UNION
    SELECT CONCAT(t.title, ' -> ', str) as str, t.prequelID
FROM (Books NATURAL JOIN Prequels) as t 
INNER JOIN series AS s ON s.prequelID = t.bookID
)
SELECT str as series FROM series
ORDER BY series;

这是结果：

我不想要任何重复，只想要显示整个系列的完整字符串。我该怎么做？

更新:

我更新了查询，因为我意识到我错过了该系列的第一本书。

WITH RECURSIVE series AS (
    SELECT CONCAT( a.title) as str, a.prequelID
    FROM ( Prequels NATURAL JOIN Books) AS a
    UNION
    SELECT CONCAT(t.title, ' -> ', str) as str, t.prequelID
FROM (Books NATURAL JOIN Prequels) as t 
INNER JOIN series AS s ON s.prequelID = t.bookID
)
SELECT CONCAT(a.title, ' -> ',a.str) as series
FROM (
SELECT Books.title, series.str
FROM series JOIN Books ON series.prequelID = Books.bookID
WHERE NOT EXISTS(
        SELECT prequelID
        FROM Prequels
        WHERE series.prequelID = Prequels.bookID
) 
) a
ORDER BY series;

结果还是有点偏差，因为我只想要系列的完整字符串：

我该如何解决这个问题？

表格：

CREATE TABLE Books
(bookID integer PRIMARY KEY,
title varchar(100),
pages integer);


CREATE TABLE Prequels
(bookID INTEGER REFERENCES Books(bookID),
prequelID INTEGER REFERENCES Books(bookID),
PRIMARY KEY (bookID,prequelID));

《权力的游戏》系列示例数据：

INSERT INTO BOOKS (bookID,title,pages) VALUES (80429,'A Game of Thrones',292);
INSERT INTO BOOKS (bookID,title,pages) VALUES (41121,'A Clash of Kings',160);
INSERT INTO BOOKS (bookID,title,pages) VALUES (29287,'A Storm of Swords',160);
INSERT INTO BOOKS (bookID,title,pages) VALUES (17696,'A Feast for Crows',292);
INSERT INTO BOOKS (bookID,title,pages) VALUES (3947,'A Dance with Dragons',101);


INSERT INTO Prequels (bookID,prequelID) VALUES (41121,80429);
INSERT INTO Prequels (bookID,prequelID) VALUES (29287,41121);
INSERT INTO Prequels (bookID,prequelID) VALUES (17696,29287);
INSERT INTO Prequels (bookID,prequelID) VALUES (3947,17696);

Answer 1

递归查询后，可以将所有str与自连接进行比较，保留不属于任何[=12的子串的s1.str =] 感谢 WHERE s2.str IS NULL 子句。

WITH RECURSIVE series AS (
    SELECT CONCAT( a.title) as str, a.prequelID
    FROM ( Prequels NATURAL JOIN Books) AS a
    UNION
    SELECT CONCAT(t.title, ' -> ', str) as str, t.prequelID
FROM (Books NATURAL JOIN Prequels) as t 
INNER JOIN series AS s ON s.prequelID = t.bookID
)
SELECT s1.str as series 
  FROM series AS s1
  LEFT JOIN series AS s2
    ON s2.str ~ s1.str
   AND s2.str <> s1.str
 WHERE s2.str IS NULL
ORDER BY series;

测试结果在dbfiddle

Answer 2

你想从树根开始。
prequelId 中没有根。

WITH RECURSIVE series AS (
    SELECT 
      b.bookId
    , 1 as lvl
    , p.prequelID
    , CONCAT(b.title) as series
    FROM Books AS b
    LEFT JOIN Prequels AS p 
      ON p.bookId = b.bookId
    WHERE NOT EXISTS (
      SELECT 1
      FROM Prequels p2
      WHERE p2.prequelID = b.bookId
    )
    
    UNION ALL
    
    SELECT 
      s.bookId
    , s.lvl+1
    , p.prequelID
    , CONCAT(b.title, ' -> ', s.series)
    FROM series AS s
    JOIN Books AS b 
      ON b.bookId = s.prequelID
    LEFT JOIN Prequels AS p 
      ON p.bookId = s.prequelID
)
SELECT series
FROM series
WHERE prequelId is null
  AND lvl > 1
ORDER BY series;

series
A Game of Thrones -> A Clash of Kings -> A Storm of Swords -> A Feast for Crows -> A Dance with Dragons

演示 db<>fiddle here

Answer 3

LukStorms 修改版现已删除答案...

https://dbfiddle.uk/?rdbms=postgres_14&fiddle=4e26beed430aefb60f1dc91766db13d3

WITH RECURSIVE series AS (
   SELECT
      b.bookId,
      1 as lvl,
      p.prequelID,
      CONCAT(b.title)   AS series
    FROM
      books      b
    LEFT JOIN
      prequels   p
        ON p.bookid = b.bookid
    WHERE NOT EXISTS (
      SELECT 1
      FROM Prequels p
      WHERE p.prequelID = b.bookId
    )

    UNION ALL

    SELECT
      b.bookid,
      lvl+1,
      p.prequelID,
      CONCAT(b.title, ' -> ', s.series)
    FROM
      series     s
    INNER JOIN
      books      b
        ON b.bookid = s.prequelid
    LEFT JOIN
      prequels   p
        ON p.bookid = b.bookid
)
SELECT
  s.series
FROM
  series s
WHERE
  s.prequelid IS NULL
ORDER BY
  s.series;

CTE 的非递归部分有一个 LEFT JOIN，以便包括不属于系列的书籍，只是一本独立的书籍。如果您不想要，请将其恢复为 NATURAL 或 INNER JOIN。

CTE 的非递归部分有一个 WHERE 子句，以确保它只从系列的最后一本书开始。

CTE 的递归部分在前传中有一个 LEFT JOIN table，因此系列中的第一本书不会丢失（由于没有前传行），因此记录本书的前传为 NULL。

外部查询然后查找该 NULL，因此只输出已完成系列的行。

从递归查询中删除行

Remove rows from recursive query

sql

postgresql

recursive-query