mysql重复记录查询解决方法

mysql重复记录查询

1.一个字段重复，如果记录多于2天，最多只显示2条

2.sql语句

SQL code


  

CREATE TABLE `teacher` (
  `ID` bigint(20) NOT NULL COMMENT 'ID',
  `REGNAME` char(200) DEFAULT NULL COMMENT '师教编号',
  `NAME` char(20) NOT NULL COMMENT '教师名称',
  `TYPE` int(1) DEFAULT '0' COMMENT '师教类型（0：内聘，1：外聘）',
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `teacher` VALUES ('10001', 'allen', 'allen', '0');
INSERT INTO `teacher` VALUES ('10002', 'ruby', 'ruby', '0');
INSERT INTO `teacher` VALUES ('10003', 'sharon', 'sharon', '1');
INSERT INTO `teacher` VALUES ('10004', 'alpha', 'alpha', '0');
INSERT INTO `teacher` VALUES ('10005', 'alpha', 'alpha', '0');
INSERT INTO `teacher` VALUES ('10006', 'alpha', 'alpha', '0');

1.数据库记录

2.需要的结果

SELECT * FROM `teacher`;

SELECT * FROM `teacher` A WHERE 2>=(SELECT COUNT(*) FROM `teacher`

WHERE A.`NAME`=`NAME` AND A.`ID`>=`ID`

)

在Oracle中可以这样

查询所有有重复字段的所有记录

select * from teacher A where (select count(*) from teacher where A.NAME=NAME )>=2;

而后查询前两条记录

SELECT * FROM (select * from teacher A where (select count(*) from teacher where A.NAME=NAME )>=2) E1 WHERE

(SELECT COUNT(*) FROM (select * from teacher A where (select count(*) from teacher where A.NAME=NAME )>=2) E2 WHERE E1.NAME=E2.NAME AND E2.ID<E1.ID )<2 order by NAME,ID;

这样也可以的：

SQL code


SELECT a.id,a.regname,a.name,a.type 
FROM teacher a 
LEFT JOIN teacher b 
ON b.name=a.name AND b.id>a.id 
GROUP BY a.id,a.regname,a.name,a.type 
HAVING COUNT(b.id) < 2;




  
  
   
   SQL code
   
   mysql> select * from teacher;
+-------+---------+--------+------+
| ID    | REGNAME | NAME   | TYPE |
+-------+---------+--------+------+
| 10001 | allen   | allen  |    0 |
| 10002 | ruby    | ruby   |    0 |
| 10003 | sharon  | sharon |    1 |
| 10004 | alpha   | alpha  |    0 |
| 10005 | alpha   | alpha  |    0 |
| 10006 | alpha   | alpha  |    0 |
+-------+---------+--------+------+
6 rows in set (0.00 sec)

mysql> select * from teacher t
    -> where 2>(select count(*) from teacher where REGNAME=t.REGNAME and ID<t.ID);
+-------+---------+--------+------+
| ID    | REGNAME | NAME   | TYPE |
+-------+---------+--------+------+
| 10001 | allen   | allen  |    0 |
| 10002 | ruby    | ruby   |    0 |
| 10003 | sharon  | sharon |    1 |
| 10004 | alpha   | alpha  |    0 |
| 10005 | alpha   | alpha  |    0 |
+-------+---------+--------+------+
5 rows in set (0.02 sec)

mysql>


SELECT A.NAME,COUNT(*) FROM `teacher` A  
LEFT JOIN `teacher` B
ON A.`NAME`=B.`NAME` AND A.`ID`>=B.`ID`
看看结果

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