清理数据库中的冗余数据 [英] cleaning up db of redundant data

问题描述

locid   country city
39409   US  Aaronsburg
128426  US  Aaronsburg
340356  US  Aaronsburg
429373  US  Aaronsburg
422717  US  Abbeville
431344  US  Abbeville
433062  US  Abbeville
341726  US  Abbeville
421248  US  Abbeville
40779   US  Abbeville
326718  US  Abbeville
317654  US  Abbeville
16707   US  Abbeville
25771   US  Abbeville
120301  US  Abbeville
132115  US  Abbeville
121770  US  Abbeville
130397  US  Abbeville
5585    US  Abbeville
10227   US  Abbeville
190173  US  Abbeville
491120  US  Abbeville
311174  US  Abbeville
306532  US  Abbeville
164271  US  Abbot
465218  US  Abbot
58452   US  Abbotsford
359399  US  Abbotsford
309116  US  Abbotsford
8169    US  Abbotsford

有人可以给我一个SQL查询来帮助我清理此表吗? 在清除locid(索引)后，应重新设置，这是一个使用此查询 SELECT locid, country, city FROM location WHERE country = 'US' ORDER BY city ASC 的县城.当我通过phpmyadmin的导入多次导入sql文本时，就产生了这种冗余数据，这就是结果，

can someone give me an sql query to help me clean up this table? after clean up locid(the index) should be resetted, btw this is a county city using this query SELECT locid, country, city FROM location WHERE country = 'US' ORDER BY city ASC . this redundant data came about when i imported an sql text many times through phpmyadmin's import and this is the result,

推荐答案

在表位置添加唯一索引，这样就不会插入重复的记录

Add unique index on table location so that no duplicate records will get inserted

ALTER IGNORE TABLE location ADD UNIQUE KEY ix1(country, city);

这将自动从表中删除重复的记录，对于以后的插入查询，您需要使用INSERT IGNORE子句，以避免出现重复的错误.

This will automatically remove duplicate records from the table and for future insert queries you need to use INSERT IGNORE clause to avoid getting duplicate errors.

，但正如@AD7six在注释中所建议的那样，它可能不适用于MySQL版本5.1.41,5.5.1-m2, 6.0:请参见bug 此处

but as suggested by @AD7six in comments, it might not work on MySQL versions 5.1.41,5.5.1-m2, 6.0: see bug here

或使用DELETE查询删除重复项的另一种安全方法:

or alternate safe way to remove duplicates using DELETE query:

DELETE a
FROM location a
     LEFT JOIN (
                SELECT locid
                FROM location
                GROUP BY country, city
               )b
               ON a.locid = b.locid
WHERE b.locid IS NULL;

要重新设置auto_increment列locid的值，只需将primary key放在locid上并重新创建它即可:

to resettle values of auto_increment column locid, you can just drop the primary key on locid and recreate it:

ALTER TABLE location DROP column locid;
ALTER TABLE location 
      ADD COLUMN locid INT unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY FIRST;

或使用UPDATE查询重新设置locid值的替代方法:

or alternative way to resettle values of locid using UPDATE query:

SET var_locid = 0;

UPDATE location
SET locid = (@var_locid := @var_locid + 1)
ORDER BY locid ASC;

这篇关于清理数据库中的冗余数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！