Question

我有一个位置mysql db包含3列

Country     State           City
US          California      Los Angeles
AU          Queensland      Brisbane
AU          Victoria        Southbank
AU          Queensland      Brisbane

如何删除mysql查询中的重复行？

DELETE FROM location WHERE country IN (
  SELECT * FROM table_name 
  GROUP BY country, state, city 
  HAVING COUNT(*) >
);

我尝试了这个查询，但它没有工作

Answer 1

选择不同的行并将它们放在一个新表中：

CREATE TEMPORARY TABLE location_temp AS SELECT DISTINCT * FROM location

截断表：

DELETE FROM location;

从表中填充不同的值

INSERT INTO location(Country, State, City) SELECT Country, State, City FROM location_temp;

资源：http://www.databasejournal.com/features/mysql/article.php/2201621/Deleting-Duplicate-Rows-in-a-MySQL-Database.htm

Answer 2

您的查询有很多问题：

DELETE FROM location
where country in (SELECT *
                  FROM table_name 
                  GROUP BY country, state, city 
                  having COUNT(*)>);

例如：（1）您从子查询返回多个列，但只与一列进行比较。（2）比较后你没有号码。（3）它指的是两个不同的表格。

数据的结构方式（行上没有唯一ID），确定要删除的行很困难。我建议你改用truncate方法。然后学会在每个表中添加一个自动递增ID：

create temporary table tmpLocation as
    select country, state, city from location;

truncate table location;

insert into location(country, state, city)
    select distinct country, state, city
    from tmpLocation;

drop table tmpLocation;

在具有大量删除的大型表上，这也更有效。

Answer 3

您忘了提及count(*)>1

DELETE FROM location
where country in (
SELECT *
FROM table_name 
GROUP BY country, state, city 
having COUNT(*)>1);

仅供参考。您还可以使用ALTER IGNORE TABLE删除重复项。

这样的事情： -

ALTER IGNORE TABLE location ADD UNIQUE INDEX (COLUMN1, COLUMN2)

Answer 4

您必须使用 ALTER查询

删除重复的行

ALTER IGNORE TABLE location ADD UNIQUE INDEX index_name(Country, State, City);

或otherwise您可以使用下面的查询语法

删除重复的行

DELETE
FROM table_name
WHERE col1 IN  (  
    SELECT MAX(col1)
    FROM tab_name
    GROUP BY col1, col2, col3, ....
    HAVING COUNT(*) > 1)

删除mysql中的重复行

4 个答案: