Mysql主键索引创建的实例

1、在上面了解了Mysql常见的索引后,这里进行Mysql索引实例的创建.

2、主键索引

     2.1 在创建表的时候,指定主键索引

create table table_primarykey
(   id int primary key auto_increment  ,
    name varchar(20)
);

   利用 show  create  table  table_primarykey ;   来查看表的创建语句

+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table            | Create Table                                                                                                                                                    |
+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| table_primarykey | CREATE TABLE `table_primarykey` (
  `id` int(11) NOT NULL DEFAULT '0',
  `name` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+

    2.2先创建表,在增加主键索引

create table table_primarykey
(   id int  auto_increment  ,
    name varchar(20)
);

alter table table_primarykey
add primary key (id);

利用 show  create  table  table_primarykey ;   来查看表的创建语句

+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table            | Create Table                                                                                                                                                    |
+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| table_primarykey | CREATE TABLE `table_primarykey` (
  `id` int(11) NOT NULL DEFAULT '0',
  `name` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+

3、查看表上的索引     

show indexes from table_primarykey;

执行的结果如下:

+------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table            | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table_primarykey |          0 | PRIMARY  |            1 | id          | A         |           0 | NULL     | NULL   |      | BTREE      |         |               |
+------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+