工做中,咱們常常有須要刪除一些重複數據的這種需求。重複數據多是程序bug形成的數據庫
好,讓咱們看看如何刪除這些重複數據ide
刪除重複數據的思路呢,是這樣的,查看根據這個重複字段分組後的結果有沒有大於1的狀況
若是有大於的1的狀況呢,那就說明是有重複數據的!3d
1) 建立數據庫code
create database ceshi;
2) 建立表blog
CREATE TABLE t1 ( id int(10) unsigned NOT NULL AUTO_INCREMENT, name varchar(20) not null, createdAt timestamp NOT NULL DEFAULT current_timestamp(), updatedAt timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(), PRIMARY KEY (id) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4;
3) 插入數據insert into t1 values(null,'haha',now(),now()),(null,'haha',now(),now()),(null,'xixi',now(),now()),(null,'heihei',now(),now()),(null,'hoho',now(),now()),(null,'hoho',now(),now()),(null,'sasa',now(),now()),(null,'haha',now(),now()),(null,'sasa',now(),now()),(null,'xixi',now(),now());
it
4) 查看數據select * from t1;
table
5) 根據最小id,重複字段name分組,假設咱們的需求就是最後要保留第最小id的這些數據,把其它重複的刪除
select min(id),name from t1 group by name having count(name)>1 order by id;class
6) 使用別名關聯一下,這些數據就是重複的,最後要刪除的
select a.*
from t1 a,(select *,min(id) from t1 group by name having count(name)>1)as b where a.name=b.name and a.id>b.id;date
7) 記得先備份一下數據
create table bak_t1_20190621 like t1;select
insert into bak_t1_20190621 select * from t1;
8) 刪除數據
delete a from t1 a,(select *
,min(id) from t1 group by name having count(name)>1)as b where a.name=b.name and a.id>b.id;
9) 最後檢查一下,確實已經沒有重複數據了