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MySQL仅从数据库中选择重复记录并显示计数？

2024-04-29 10:10:05 422

要仅从数据库中选择重复记录并显示计数，请使用HAVING以及聚合功能count()。让我们首先创建一个表-

mysql> create table duplicateRecords
   -> (
   -> ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> ClientName varchar(20)
   -> );

以下是使用insert命令在表中插入记录的查询-

mysql> insert into duplicateRecords(ClientName) values('John');
mysql> insert into duplicateRecords(ClientName) values('Carol');
mysql> insert into duplicateRecords(ClientName) values('John');
mysql> insert into duplicateRecords(ClientName) values('Sam');
mysql> insert into duplicateRecords(ClientName) values('Sam');
mysql> insert into duplicateRecords(ClientName) values('Bob');
mysql> insert into duplicateRecords(ClientName) values('John');
mysql> insert into duplicateRecords(ClientName) values('Sam');

以下是使用select语句显示表中所有记录的查询-

mysql> select * from duplicateRecords;

这将产生以下输出-

+----------+------------+
| ClientId | ClientName |
+----------+------------+
| 1        | John       |
| 2        | Carol      |
| 3        | John       |
| 4        | Sam        |
| 5        | Sam        |
| 6        | Bob        |
| 7        | John       |
| 8        | Sam        |
+----------+------------+
8 rows in set (0.00 sec)

以下是查询：仅从数据库中选择重复记录-

mysql> select ClientName,count(*) as DuplicateRecord
   -> from duplicateRecords
   -> group by ClientName
   -> having DuplicateRecord > 1;

这将产生以下输出-

+------------+-----------------+
| ClientName | DuplicateRecord |
+------------+-----------------+
| John       | 3               |
| Sam        | 3               |
+------------+-----------------+
2 rows in set (0.00 sec)

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MySQL仅从数据库中选择重复记录并显示计数？

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