Question

可能重复：
How to delete duplicate rows with SQL?

我有这个查询，它以相同的名称和年份从表中返回重复的行。

如何删除重复记录，因此表中只有唯一值？

查询是：

SELECT movies.movie_name, movies.year 
FROM movies
INNER JOIN 
(
    SELECT movie_name, year 
    FROM movies
    GROUP BY movie_name,year 
    HAVING count(movie_id) > 1
) dup 
    ON movies.movie_name = dup.movie_name
    and movies.year = dup.year

Answer 1

DELETE语句可以使用子查询来过滤要删除的项目。

通读本

http://www.w3resource.com/sql/delete-statement/delete-with-subqueries.php

Answer 2

此查询显示所有重复项：

SELECT movie_name, year 
FROM movies
GROUP BY movie_name,year 
HAVING count(movie_id) > 1

这只显示每部电影的movie_id（重复或不重复），这些是要保留的行：

SELECT movie_name, year, min(movie_id) min_movie_id
FROM movies
GROUP BY movie_name,year

要删除重复项，您可以使用：

DELETE movies
FROM
  movies inner join
  (SELECT movie_name, year, min(movie_id) min_movie_id
   FROM movies
   GROUP BY movie_name,year) keep
  on movies.movie_name = keep.movie_name
     and movies.year=keep.year
     and movies.movie_id<>keep.min_movie_id

或者您也可以使用此查询：

delete from movies
where
  (movie_name, year, movie_id) not in
  (select movie_name, year, min_movie_id from
    (SELECT movie_name, year, min(movie_id) min_movie_id
     FROM movies
     GROUP BY movie_name,year) keep)

删除重复的行？

2 个答案: