用于在列中查找不同值并获取总和的 MySQL 查询

Question

我的电影 DVD 很少，想在 MySQL 中创建一个简单的数据库。 PF 数据库结构。我有一个 MySQL 查询，实际上没有列出确切的编号。我正在看的电影。下面的查询是 -

SELECT SUM(Total) as total
FROM (
SELECT COUNT(DISTINCT(Movie1)) AS Total FROM tbl_movie 
      WHERE Movie1 !='' AND Movie1 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT COUNT(DISTINCT(Movie2)) FROM tbl_movie 
       WHERE Movie2 !='' AND Movie2 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT COUNT(DISTINCT(Movie3)) FROM tbl_movie 
       WHERE Movie3 !='' AND Movie3 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT COUNT(DISTINCT(Movie4)) FROM tbl_movie 
       WHERE Movie4 !='' AND Movie4 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT COUNT(DISTINCT(Movie5)) FROM tbl_movie 
       WHERE Movie5 !='' AND Movie5 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT COUNT(DISTINCT(Movie6)) FROM tbl_movie 
       WHERE Movie6 !='' AND Movie6 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT COUNT(DISTINCT(Movie7)) FROM tbl_movie 
       WHERE Movie7 !='' AND Movie7 IS NOT NULL AND DVDCategory='Movie'
) AS Total;

数据库结构-

ID DVD Movie1   Movie2   Movie3      Movie4          Movie5   Movie6   Movie7
__________________________________________________________________
1  1  IronMan  Movie11   MindHunters  300            Jumper   7        
2  2  IronMan2 Movie22   Grey         Blood Diamond
3  3  Movie33  Red Eye   Departed     300            
4  4  Movie44  Gladiator King Kong
5  5  Movie55  Hitman

它在 DB 中显示 13 个结果而不是 18 个电影。我搜索了您的问题列表，但没有找到合适的答案。您能否说明我哪里出错了，或者有什么更好的方法可以安排此查询？

Answer 1

更新 -

UNION 出错了。它删除重复项。您的内部查询返回 (5,5,4,2,1,1,0) 但在删除重复项后联合将它们变成 (5,4,2,1,0)。

您需要使用UNION ALL 来计算所有内容。只需将所有 UNION 替换为 UNION ALL

当您这样做时，您会注意到如果跨列有电影，即如果电影 300 在 Movie4 和 Movie5 列中用于不同的用户，它将计算两次。

如果您只需要在所有列中获取不同的电影，请先从各个列中获取不同的电影，UNION 它们以删除重复项，然后对电影进行计数。

SELECT COUNT(movie) as total
FROM (
SELECT DISTINCT Movie1 AS movie FROM tbl_movie 
    WHERE Movie1 !='' AND Movie1 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT DISTINCT Movie2 FROM tbl_movie 
    WHERE Movie2 !='' AND Movie2 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT DISTINCT Movie3 FROM tbl_movie 
     WHERE Movie3 !='' AND Movie3 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT DISTINCT Movie4 FROM tbl_movie 
     WHERE Movie4 !='' AND Movie4 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT DISTINCT Movie5 FROM tbl_movie 
     WHERE Movie5 !='' AND Movie5 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT DISTINCT Movie6 FROM tbl_movie 
     WHERE Movie6 !='' AND Movie6 IS NOT NULL AND DVDCategory='Movie'
UNION
SELECT DISTINCT Movie7 FROM tbl_movie 
     WHERE Movie7 !='' AND Movie7 IS NOT NULL AND DVDCategory='Movie'
) AS AllDistinctMovies;