Question

我目前正在完成sqlzoo的More JOIN operations教程，并遇到以下代码作为＃12的答案：

SELECT yr,COUNT(title) 
FROM movie 
JOIN casting 
JOIN actor   
ON actorid=actor.id AND movie.id=movieid
WHERE name='John Travolta'
GROUP BY yr

HAVING COUNT(title)=
(SELECT MAX(c) FROM
(SELECT yr, COUNT(title) AS c 
FROM movie 
JOIN casting ON movie.id=movieid
JOIN actor   ON actorid=actor.id
WHERE name='John Travolta'
GROUP BY yr) AS t
)

是否有更简洁的方式来表达此代码？

Answer 1

是。如果我正确理解问题，那就更简单了。

SELECT yr,COUNT(title) 
   FROM movie JOIN casting ON movie.id=movieid
        JOIN 
        actor   ON actorid=actor.id
WHERE name='John Travolta'
GROUP BY yr
HAVING COUNT(title) > 2

Answer 2

看起来原始网站的建议答案与他们提出的问题不符。

他们问的最佳答案：

SELECT yr,COUNT(title) FROM
  movie JOIN casting ON movie.id=movieid
         JOIN actor   ON actorid=actor.id
WHERE name='John Travolta'
GROUP BY yr
HAVING COUNT(title)>2

他们的回答是：

SELECT yr,COUNT(title) FROM
movie JOIN casting ON movie.id=movieid
JOIN actor ON actorid=actor.id
WHERE name='John Travolta'
GROUP BY yr
HAVING COUNT(title)=
(SELECT MAX(c) FROM (SELECT yr,COUNT(title) AS c 
FROM movie 
JOIN casting ON movie.id=movieid JOIN actor ON actorid=actor.id
WHERE name='John Travolta'
GROUP BY yr) AS t

）

但这实际上回答了一个不同的问题，即：“他制作电影的时间最多，那年是哪一年，他制作了多少部电影？”

编写HAVING条件的最有效方法

2 个答案: