INNER JOIN中的子查询(MySQL)

Question

我似乎在内连接中有一个子查询有问题,但是我没有.

• 服务器:通过UNIX套接字的Localhost
• 软件:MySQL
• 软件版本:5.5.32-nmm2-log - (Ubuntu)
• 数据库客户端版本:libmysql - 5.5.32

有一个m:n表构造,有3个表,其中只有2个与问题相关.

• 第一个是包含actor的表,标识符:caid.
• 第二个是跨表连接演员到电影(演员ID:caid,电影ID:id)

当我像这样创建一个完整的内部联接:

SELECT count( * ) AS Count, lastname, firstname
FROM DVDPROFILER_dvd_common_actor
INNER JOIN DVDPROFILER_dvd_actor ON DVDPROFILER_dvd_common_actor.caid = DVDPROFILER_dvd_actor.caid
WHERE DVDPROFILER_dvd_actor.caid > 0
GROUP BY DVDPROFILER_dvd_actor.caid
ORDER BY Count DESC 

我得到的正是我所期待的:顶级演员按照他在任何电影中记入的时间计算,即使多次担任多个角色也是如此.

我的目标是提取有关演员被分析的电影的数量的信息,我认为 - 我很天真 - 它应该像这样简单:

SELECT count( * ) AS Count, lastname, firstname
FROM DVDPROFILER_dvd_common_actor
INNER JOIN
  (SELECT caid
  FROM DVDPROFILER_dvd_actor
  GROUP BY id) AS DVDPROFILER_dvd_actor 
ON DVDPROFILER_dvd_common_actor.caid = DVDPROFILER_dvd_actor.caid
WHERE DVDPROFILER_dvd_actor.caid > 0
GROUP BY DVDPROFILER_dvd_actor.caid
ORDER BY Count DESC 

但结果完全不正确

所以我用一个选定的actor检查了子查询

SELECT caid, id
FROM DVDPROFILER_dvd_actor
WHERE caid = 30801
GROUP BY id

并得到我所期望的

所以我玩了一下,当我在子查询中引入LIMIT子句时,我突然得到了不同但从未正确的回复.

SELECT count( * ) AS Count, lastname, firstname
FROM DVDPROFILER_dvd_common_actor
INNER JOIN 
  (SELECT caid
  FROM DVDPROFILER_dvd_actor
  GROUP BY id
  LIMIT 0 , 50000) AS DVDPROFILER_dvd_actor 
ON DVDPROFILER_dvd_common_actor.caid = DVDPROFILER_dvd_actor.caid
WHERE DVDPROFILER_dvd_actor.caid > 0
GROUP BY DVDPROFILER_dvd_actor.caid
ORDER BY Count DESC 

对于不同的LIMIT,我得到了不同的结果,但在某些时候,当我超过一定限度时,结果完全没有限制 - 但同样错误.

我在这里俯瞰什么？:-(

Answer 1

你能试试吗？我想COUNT(DISTINCT DVDPROFILER_dvd_actor.id)对你有帮助.

SELECT lastname, firstname, COUNT(DISTINCT DVDPROFILER_dvd_actor.id) AS Count
FROM DVDPROFILER_dvd_common_actor
INNER JOIN DVDPROFILER_dvd_actor ON DVDPROFILER_dvd_common_actor.caid = DVDPROFILER_dvd_actor.caid
WHERE DVDPROFILER_dvd_actor.caid > 0
GROUP BY lastname, firstname
ORDER BY Count DESC 

如果没有,我们非常高兴您在http://www.sqlfiddle.com/上发布数据和架构.这使我们更容易测试

谢谢.