Create index < index name > on < table name > (< column name > [<; Length >] [American DESC])

Limitation: Only ordinary indexes and unique indexes can be added; Cannot create primary key index.

Second, the method of changing the table.

Change table < table name > add index [<; Index name >] (<; Column name >, ...)

Change table < table name > add unique [index | key] [<; Index name >] (<; Column name >, ...)

Change table < table name > add primary key (< column name >, …)

Change table < table name > Add foreign key [<; Index name >] (<; Column name >, ...)

Third, when CREATE TABLE is specified.

Create a universal index

Create table tb_stu_info

(

Id INT is not empty.

Name CHAR(45) is empty by default.

Dept_id INT is empty by default.

Age INT defaults to NULL.

Height INT defaults to NULL,

Index (height)

);

Create a unique index

Mysql & gt creates table tb_stu_info2.

(

Id INT is not empty.

Name CHAR(45) is empty by default.

Dept_id INT is empty by default.

Age INT defaults to NULL.

Height INT defaults to NULL,

Unique index (height)

);

Create a primary key (although ALTER TABLE can also be created, the primary key is usually created when the table is created).

Create table mytable (

ID INT is not empty.

User name VARCHAR( 16) is not empty.

Primary key (ID)

);