Question

我正在尝试创建一个以超过X种语言制作电影的演员排名，这是我的架构：

actor( actorid, actorname)
act ( actoirid, movieid, as_character)
movie ( movieid, title, mvyear)
lang (movieid, lang)

这是我坚持的查询：

SELECT actorid, actorname, title, mvyear, as_character, lang 
FROM actor NATURAL JOIN act NATURAL JOIN movies_slice NATURAL JOIN lang
WHERE actorid IN (
    SELECT act.actorid FROM act NATURAL JOIN lang 
    GROUP BY (act.actorid) HAVING COUNT(DISTINCT lang.lang)  > $X$
    ORDER BY COUNT(DISTINCT lang.lang) DESC --<<< Want to keep this order.
)

我知道IN运算符右侧的子查询的顺序被丢弃了。我该如何解决这个问题？

Answer 1

永远不要使用NATURAL JOIN。这是一个等待发生的错误。连接键是匹配的任何列名称 - 它甚至不遵循声明的外键关系。并且，查询很难遵循，因为您不知道用于加入的键。

然后，要执行您想要的操作，请将子查询移动到FROM子句，将计数计算为字段，然后按顺序执行：

SELECT a.actorid, a.actorname, m.title, m.mvyear, act.as_character, l.lang 
FROM actor a JOIN
     act
     USING (actorid) JOIN
     movies m
     USING (movieid) JOIN
     lang l
     USING (movieid) JOIN
     (SELECT act.actorid, COUNT(DISTINCT l.lang) as numlangs
      FROM act JOIN
           lang l
           USING (movieid)
      GROUP BY act.actorid
      HAVING COUNT(DISTINCT l.lang) > $X$
     ) al
     USING (actorid)
ORDER BY al.numlangs DESC;

Postgresql - 使用IN运算符保持子查询的顺序

1 个答案: