Question

我有一个棒球运动员表（全部1000左右），有字段：

mysql> describe person;
+-----------+-------------+------+-----+---------+----------------+
| Field     | Type        | Null | Key | Default | Extra          |
+-----------+-------------+------+-----+---------+----------------+
| id        | int(11)     | NO   | PRI | NULL    | auto_increment |
| firstname | varchar(30) | NO   |     | NULL    |                |
| lastname  | varchar(30) | NO   |     | NULL    |                |
+-----------+-------------+------+-----+---------+----------------+

但我认为有些球员已经两次加入。我如何查看特定名字，姓氏组合的出现次数？

Answer 1

这提供了重复列表：

SELECT firstname, lastname, COUNT(*) 
FROM person 
GROUP BY firstname, lastname 
HAVING COUNT(*) > 1;

如果要查看每行的计数，请删除having子句：

SELECT firstname, lastname, COUNT(*) 
FROM person 
GROUP BY firstname, lastname;

Answer 2

SELECT firstname, lastname, count(id) count
  FROM person
 WHERE firstname = ?
   AND lasttname = ?
 GROUP BY firstname, lastname

Answer 3

对于按减少的份数值排序的列表：

SELECT firstname, lastname, COUNT(*) AS n
  FROM person
 GROUP BY firstname, lastname
 ORDER BY n DESC
 HAVING n > 1

HAVING子句是关键部分 - 必须在 GROUP BY子句后过滤结果，因为WHERE子句过滤掉行之前他们被分组。

Answer 4

要获取重复名称和名称的ID，请执行以下操作：

SELECT p1.id, p1.firstname, p1,lastname FROM person p1
INNER JOIN person p2 ON (p1.firstname = p2.firstname 
                         AND p1.lastname = p1.lastname 
                         AND p1.id <> p2.id);

Answer 5

如果您只想删除所有副本，可以使用临时表格填写所有re data except the duplicate and them re-update you主表格。

选择具有重复数据的查询将是

 SELECT DISTINCT firstname, lastname FROM table

获取表格中的完整数据列表

SELECT firstname, lastname, COUNT(*) AS n
  FROM person
 GROUP BY firstname, lastname
 ORDER BY lastname DESC
 HAVING n > 1

使用最后一个查询，您将获得按姓氏字节排序的数据列表。

Answer 6

To find duplicate records (ex: to find login name and password combination of duplicate records) in a table use the below query;

SELECT em.* FROM employee_master AS em JOIN 
 (SELECT emp.login, emp.password, COUNT(*) 
  FROM employee_master emp 
  WHERE emp.login != '' AND emp.password != '' 
  GROUP BY emp.login, emp.PASSWORD
  HAVING COUNT(*) > 1
 ) AS dl 
WHERE em.login =  dl.login AND em.password = dl.password;

如何在多列上检查mysql表中的重复项

6 个答案: