Mysql中查找並刪除重復數據的方法

本文章介紹重復數據刪除方法包括單字段與多字段重復數據查詢刪除方法，最後還寫了一個存儲過程希望文章對各位朋友會帶來幫助。

(一)單個字段

1、查找表中多余的重復記錄，根據（question_title）字段來判斷

 代碼如下 復制代碼 select * from questions where question_title in (select question_title from people group by question_title having count(question_title) > 1)

2、刪除表中多余的重復記錄，根據（question_title）字段來判斷，只留有一個記錄

 代碼如下 復制代碼 delete from questions
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)多個字段

刪除表中多余的重復記錄（多個字段），只留有rowid最小的記錄

 代碼如下 復制代碼

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)

用上述語句無法刪除，創建了臨時表才刪的，求各位達人解釋一下。

 代碼如下 復制代碼

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) 存儲過程

 代碼如下 復制代碼

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

例,

數據庫版本 Server version: 5.1.41-community-log MySQL Community Server (GPL)

例1，表中有主鍵(可唯一標識的字段)，且該字段為數字類型

例1測試數據

 代碼如下 復制代碼

/* 表結構 */
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;

/* 插入測試數據 */
INSERT INTO `t1`(`name`,`add`) VALUES
('abc',"123"),
('abc',"123"),
('abc',"321"),
('abc',"123"),
('xzy',"123"),
('xzy',"456"),
('xzy',"456"),
('xzy',"456"),
('xzy',"789"),
('xzy',"987"),
('xzy',"789"),
('ijk',"147"),
('ijk',"147"),
('ijk',"852"),
('opq',"852"),
('opq',"963"),
('opq',"741"),
('tpk',"741"),
('tpk',"963"),
('tpk',"963"),
('wer',"546"),
('wer',"546"),
('once',"546");

SELECT * FROM `t1`;
+----+------+-----+
| id | name | add |
+----+------+-----+
|  1 | abc  | 123 |
|  2 | abc  | 123 |
|  3 | abc  | 321 |
|  4 | abc  | 123 |
|  5 | xzy  | 123 |
|  6 | xzy  | 456 |
|  7 | xzy  | 456 |
|  8 | xzy  | 456 |
|  9 | xzy  | 789 |
| 10 | xzy  | 987 |
| 11 | xzy  | 789 |
| 12 | ijk  | 147 |
| 13 | ijk  | 147 |
| 14 | ijk  | 852 |
| 15 | opq  | 852 |
| 16 | opq  | 963 |
| 17 | opq  | 741 |
| 18 | tpk  | 741 |
| 19 | tpk  | 963 |
| 20 | tpk  | 963 |
| 21 | wer  | 546 |
| 22 | wer  | 546 |
| 23 | once | 546 |
+----+------+-----+
rows in set (0.00 sec)

查找id最小的重復數據(只查找id字段)

 代碼如下 復制代碼

/* 查找id最小的重復數據(只查找id字段) */
SELECT DISTINCT MIN(`id`) AS `id`
FROM `t1`
GROUP BY `name`,`add`
HAVING COUNT(1) > 1;
+------+
| id   |
+------+
|    1 |
|   12 |
|   19 |
|   21 |
|    6 |
|    9 |
+------+
rows in set (0.00 sec)

查找所有重復數據

 代碼如下 復制代碼 /* 查找所有重復數據 */
SELECT `t1`.*
FROM `t1`,(
  SELECT `name`,`add`
  FROM `t1`
  GROUP BY `name`,`add`
  HAVING COUNT(1) > 1
) AS `t2`
WHERE `t1`.`name` = `t2`.`name`
  AND `t1`.`add` = `t2`.`add`;
+----+------+-----+

| id | name | add |
+----+------+-----+
|  1 | abc  | 123 |
|  2 | abc  | 123 |
|  4 | abc  | www.111cn.net|
|  6 | xzy  | 456 |
|  7 | xzy  | 456 |
|  8 | xzy  | 456 |
|  9 | xzy  | 789 |
| 11 | xzy  | 789 |
| 12 | ijk  | 147 |
| 13 | ijk  | 147 |
| 19 | tpk  | 963 |
| 20 | tpk  | 963 |
| 21 | wer  | 546 |
| 22 | wer  | 546 |
+----+------+-----+
rows in set (0.00 sec)