Mysql中查找並刪除重復數據的方法

 　　(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   select * from questions where question_title in (select question_title from peoplegroup 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   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  

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  

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  

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  

/* 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  

/* 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   /* 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)