mysql添加mul的语句_使用Key = MUL创建MySQL列？

董霖

2023-12-01

您需要使用ADD KEY来创建Key = MUL的列。语法如下-ALTER TABLE yourTableName MODIFY COLUMN yourColumnName data type,

ADD KEY(yourColumnName);

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 Instructor

-> (

-> Instructor_Id int,

-> Instructor_Name varchar(30),

-> Instructor_CourseName varchar(100)

-> );

现在，您可以查看表的表说明，KEY列没有任何MUL键。查询如下，以使用DESC命令检查表的描述。mysql> desc Instructor;

以下是输出-+-----------------------+--------------+------+-----+---------+-------+

+-----------------------+--------------+------+-----+---------+-------+

| Instructor_Id | int(11) | YES | | NULL | |

+-----------------------+--------------+------+-----+---------+-------+

3 rows in set (0.00 sec)

这是在MySQL中使用Key = MUL创建一列的查询。将“ Instructor_Id”列设为Key = MUL。查询如下-mysql> alter table Instructor modify column Instructor_Id int NOT NULL AUTO_INCREMENT,

-> add key(Instructor_Id);

Records: 0 Duplicates: 0 Warnings: 0

现在再次检查表说明。查询如下-mysql> desc Instructor;

以下是输出-+-----------------------+--------------+------+-----+---------+----------------+

+-----------------------+--------------+------+-----+---------+----------------+

| Instructor_Id | int(11) | NO | MUL | NULL | auto_increment |

+-----------------------+--------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)

要添加非主键，您需要使用以下查询-mysql> alter table Instructor modify column Instructor_Name varchar(30) NOT NULL,

-> add key(Instructor_Name);

Records: 0 Duplicates: 0 Warnings: 0

现在再次检查表说明。查询如下-mysql> desc Instructor;

以下是显示其中一个字段的Key为MUL的输出-+-----------------------+--------------+------+-----+---------+----------------+

+-----------------------+--------------+------+-----+---------+----------------+

| Instructor_Id | int(11) | NO | MUL | NULL | auto_increment |

+-----------------------+--------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)