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我必须制作一个递归 CTE 以将所有知道 kevin bacon 的演员还给我，以便更好地了解我的数据库一个只通过两个演员了解培根的人 例如，您可能想知道阿尔弗雷德希区柯克如何与凯文培根联系起来。一个答案是：阿尔弗雷德·希区柯克和奥森·威尔斯一起在演艺界（1943），奥森·威尔斯和杰克·尼科尔森在一个安全的地方（1971），杰克·尼科尔森和凯文·培根在几个好男人（1992） ！我正在尝试两种不同的方法，一种是给我一个空集，另一种是给我这个错误消息'递归通用表表达式 DBMASTER 的完整选择。培根”

WITH bacon (actorid, bacon_number) AS (
SELECT UNIQUE actorid, 0 FROM movies2actors 
        WHERE actorid =  (SELECT actorid FROM actors WHERE name = 'Bacon, Kevin (I)') UNION ALL
SELECT movies2actors.actorid, bacon.bacon_number + 1
FROM movies2actors, bacon 
       WHERE movies2actors.actorid IN 
            (SELECT UNIQUE actorid FROM movies2actors WHERE movieid IN (SELECT UNIQUE movieid FROM movies2actors 
                WHERE actorid = (SELECT actorid FROM actors WHERE name = 'Bacon, Kevin (I)') )) 
            AND movies2actors.actorid <> (SELECT actorid FROM actors WHERE name = 'Bacon, Kevin (I)') AND bacon.bacon_number<2  
)
SELECT bacon.actorid , bacon.bacon_number  FROM bacon ;

WITH bacon (actorid,relationid, bacon_number) AS (
SELECT UNIQUE actorid, actorid ,0 FROM ACTORS 
        WHERE name = 'Bacon, Kevin (I)'
UNION ALL
SELECT ACTORS.actorid,bacon.relationid, bacon.bacon_number + 1
FROM ACTORS
       JOIN  bacon ON ACTORS.actorid = bacon.relationid
       WHERE ACTORS.actorid IN 
            (SELECT UNIQUE actorid FROM movies2actors WHERE movieid IN (SELECT UNIQUE movieid FROM movies2actors 
                WHERE actorid = (SELECT actorid FROM actors WHERE name = 'Bacon, Kevin (I)') )) 
            AND ACTORS.actorid <> (SELECT actorid FROM actors WHERE name = 'Bacon, Kevin (I)') AND bacon.bacon_number<2     
)
SELECT bacon.actorid , bacon.bacon_number  FROM bacon ;
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2 回答 2

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在递归 CTE 中使用旧的连接语法（在 Db2 LUW 中）

table a,
table b
Where a.col = b.col
于 2019-12-18T19:04:15.650 回答
0

尝试这个：

/*
WITH 
  Movies (movieid, moviename) AS 
(
 VALUES
   (1, 'Show Business at War (1943)')
 , (2, 'A Safe Place (1971)')
 , (3, 'A Few Good Men (1992)')
)
, Actors (actorid, actorname) AS 
 (
 VALUES
   (1, 'Alfred Hitchcock')
 , (2, 'Orson Welles')
 , (3, 'Jack Nicholson')
 , (4, 'Kevin Bacon')
 )
 , Movies2Actors (movieid, actorid) AS
 (
 VALUES
  (1, 1)
, (1, 2)   
, (2, 2)   
, (2, 3)   
, (3, 3)
, (3, 4)
 )
, 
*/
bacon (actorid, level, chain) AS
(
SELECT mo.actorid, 1, cast('|'||trim(a.actorid)||'|'||trim(mo.actorid)||'|' AS varchar(1000))
FROM Actors a, Movies2Actors mb, Movies2Actors mo
WHERE a.actorname=
'Kevin Bacon' 
--'Jack Nicholson'
--'Orson Welles'
AND a.actorid=mb.actorid AND mb.movieid=mo.movieid
AND a.actorid<>mo.actorid 
  UNION ALL
SELECT mo.actorid, b.level+1, b.chain||trim(mo.actorid)||'|'
FROM bacon b, Movies2Actors mb, Movies2Actors mo
WHERE b.actorid=mb.actorid AND mb.movieid=mo.movieid
AND locate('|'||trim(mo.actorid)||'|', b.chain)=0 
)
SELECT DISTINCT a.actorname
--, b.*
FROM bacon b
JOIN Actors a ON a.actorid=b.actorid;

您可以取消注释带有示例数据的注释块并按原样运行语句以检查结果。
该chain列是为了防止递归。

于 2019-12-18T20:33:47.140 回答