如何在 MySQL 中删除重复项并在表中保留一行?
mysqlmysqli database
要删除重复项并在表中保留一行，您需要使用临时表的概念。步骤如下 −
create table anytemporaryTableName as select distinct yourColumnName1, yourColumnName2 from yourTableName; truncate table yourTableName; insert into yourTableName(yourColumnName1, yourColumnName2) select yourColumnName1, yourColumnName2 from yourtemporaryTableName ; drop table yourtemporaryTableName ;
让我们创建一个表 −
mysql> create table demo39 −> ( −> user_id int, −> user_name varchar(20) −> ); Query OK, 0 rows affected (0.74 sec)
使用 insert 命令向表中插入一些记录 −
mysql> insert into demo39 values(10,'John'); Query OK, 1 row affected (0.19 sec) mysql> insert into demo39 values(10,'John'); Query OK, 1 row affected (0.13 sec) mysql> insert into demo39 values(11,'David'); Query OK, 1 row affected (0.20 sec) mysql> insert into demo39 values(11,'David'); Query OK, 1 row affected (0.17 sec)
使用 select 语句显示表中的记录 −
mysql> select *from demo39;
这将产生以下输出 −
+---------+-----------+ | user_id | user_name | +---------+-----------+ | 10 | John | | 10 | John | | 11 | David | | 11 | David | +---------+-----------+ 4 rows in set (0.00 sec)
以下是删除重复项并在表中保留一行的查询 −
mysql> create table temporaryTable as select distinct user_id, user_name from demo39; Query OK, 2 rows affected (1.39 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> truncate table demo39; Query OK, 0 rows affected (2.30 sec) mysql> insert into demo39(user_id, user_name) select user_id, user_name from temporaryTable; Query OK, 2 rows affected (0.16 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> drop table temporaryTable; Query OK, 0 rows affected (1.01 sec)
使用 select 语句显示表中的记录 −
mysql> select *from demo39;
这将产生以下输出 −
+---------+-----------+ | user_id | user_name | +---------+-----------+ | 10 | John | | 11 | David | +---------+-----------+ 2 rows in set (0.00 sec)
