如何删除 MySQL 中除一条记录之外的重复记录?
你可以使用带有某些条件的 DELETE 命令,因为我们需要保留一条记录并删除其余的重复记录。
让我们首先创建一个表 −
mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentName varchar(40) ); Query OK, 0 rows affected (0.48 sec)
使用 insert 命令插入记录到表中 −
mysql> insert into DemoTable(StudentName) values('John'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable(StudentName) values('Carol'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable(StudentName) values('Sam'); Query OK, 1 row affected (0.28 sec) mysql> insert into DemoTable(StudentName) values('Carol'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(StudentName) values('David'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable(StudentName) values('Carol'); Query OK, 1 row affected (0.26 sec)
使用 select 命令从表中显示记录 −
mysql> select *from DemoTable;
这将产生以下输出 −
+-----------+-------------+ | StudentId | StudentName | +-----------+-------------+ | 1 | John | | 2 | Carol | | 3 | Sam | | 4 | Carol | | 5 | David | | 6 | Carol | +-----------+-------------+ 6 rows in set (0.00 sec)
以下是移除除了单条记录外的重复记录的查询 −
mysql> delete tbl1 from DemoTable tbl1,DemoTable tbl2 WHERE tbl1.StudentName = tbl2.StudentName AND tbl1.StudentId > tbl2.StudentId; Query OK, 2 rows affected (0.79 sec)
上面的查询删除了“Carol”的 2 行,并留下了一条“Carol”记录。
现在,我们来显示表记录 −
mysql> select *from DemoTable;
这将产生以下输出 −
+-----------+-------------+ | StudentId | StudentName | +-----------+-------------+ | 1 | John | | 2 | Carol | | 3 | Sam | | 5 | David | +-----------+-------------+ 4 rows in set (0.00 sec)
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