MySQL 查询跳过重复项并从重复值中仅选择一个
mysqlmysqli database
语法如下，用于跳过重复值并从重复值中仅选择一个 −
select min(yourColumnName1),yourColumnName2 from yourTableName group by yourColumnName2;
为了理解上述语法，让我们创建一个表。创建表的查询如下 −
mysql> create table doNotSelectDuplicateValuesDemo -> ( -> User_Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> User_Name varchar(20) -> ); Query OK, 0 rows affected (0.78 sec)
现在，您可以使用 insert 命令在表中插入一些记录。查询如下 −
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('John');
Query OK, 1 row affected (0.15 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Carol');
Query OK, 1 row affected (0.09 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Carol');
Query OK, 1 row affected (0.17 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Carol');
Query OK, 1 row affected (0.08 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Sam');
Query OK, 1 row affected (0.28 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Mike');
Query OK, 1 row affected (0.19 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Bob');
Query OK, 1 row affected (0.16 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('David');
Query OK, 1 row affected (0.21 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Maxwell');
Query OK, 1 row affected (0.13 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Bob');
Query OK, 1 row affected (0.11 sec)
mysql> insert into doNotSelectDuplicateValuesDemo(User_Name) values('Ramit');
Query OK, 1 row affected (0.16 sec)
使用 select 语句显示表中的所有记录。查询如下 −
mysql> select *from doNotSelectDuplicateValuesDemo;
这是输出 −
+---------+-----------+ | User_Id | User_Name | +---------+-----------+ | 1 | John | | 2 | Carol | | 3 | Carol | | 4 | Carol | | 5 | Sam | | 6 | Mike | | 7 | Bob | | 8 | David | | 9 | Maxwell | | 10 | Bob | | 11 | Ramit | +---------+-----------+ 11 rows in set (0.00 sec)
以下查询用于跳过重复值并从重复值中仅选择一个 −
mysql> select min(User_Id),User_Name from doNotSelectDuplicateValuesDemo group by User_Name;
这是输出 −
+--------------+-----------+ | min(User_Id) | User_Name | +--------------+-----------+ | 1 | John | | 2 | Carol | | 5 | Sam | | 6 | Mike | | 7 | Bob | | 8 | David | | 9 | Maxwell | | 11 | Ramit | +--------------+-----------+ 8 rows in set (0.07 sec)
