Mysql中查找并删除重复数据的方法
2015-12-24 18:22
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(一)单个字段
1、查找表中多余的重复记录,根据(question_title)字段来判断
select * from questions where question_title in (select question_title from people group by question_title having count(question_title) > 1)
2、删除表中多余的重复记录,根据(question_title)字段来判断,只留有一个记录
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where peopleId in (select peopleId from people group by peopleId having count(question_title) > 1)and min(id) not in (select question_id from questions group by question_title having count(question_title)>1)
(二)多个字段
删除表中多余的重复记录(多个字段),只留有rowid最小的记录
DELETE FROM questions WHERE (questions_title,questions_scope) IN (SELECT questions_title,questions_scope FROM questions GROUP BY questions_title,questions_scope HAVING COUNT(*) > 1) AND question_id NOT IN (SELECT MIN(question_id) FROM questions GROUP BY questions_scope,questions_title
HAVING COUNT(*)>1)
用上述语句无法删除,创建了临时表才删的,求各位达人解释一下。
CREATE TABLE tmp AS SELECT question_id FROM questions WHERE (questions_title,questions_scope) IN (SELECT questions_title,questions_scope FROM questions GROUP BY questions_title,questions_scope HAVING COUNT(*) > 1) AND question_id NOT IN (SELECT MIN(question_id)
FROM questions GROUP BY questions_scope,questions_title HAVING COUNT(*)>1);
DELETE FROM questions WHERE question_id IN (SELECT question_id FROM tmp);
DROP TABLE tmp;
(三) 存储过程
declare @max integer,@id integer
declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >; 1
open cur_rows
fetch cur_rows into @id,@max
while @@fetch_status=0
begin
select @max = @max -1
set rowcount @max
delete from 表名 where 主字段 = @id
fetch cur_rows into @id,@max
end
close cur_rows
set rowcount 0
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例,
数据库版本 Server version: 5.1.41-community-log MySQL Community Server (GPL)
例1,表中有主键(可唯一标识的字段),且该字段为数字类型
例1测试数据
/* 表结构 */
DROP TABLE IF EXISTS `t1`;
CREATE TABLE IF NOT EXISTS `t1`(
`id` INT(1) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(20) NOT NULL,
`add` VARCHAR(20) NOT NULL,
PRIMARY KEY(`id`)
)Engine=InnoDB;
/* 插入测试数据 */
INSERT INTO `t1`(`name`,`add`) VALUES