Reference to the following collation

Mysql Common Command Line Complete

1. Connect mysql

Format: mysql-h host address-u username-p user password

1. MYSQL connected to the local computer. (Assuming that both user name and password are root)
Firstly, open the DOS window, switch to the directory mysql bin, then type the command mysql-u root-p, enter the password root after return, and then return; or directly type the command mysql-uroot-proot to return;
Note: User name space is optional, but there must be no space before password, otherwise enter password again.
If MYSQL has just been installed, the superuser root has no password, so you can enter MYSQL directly by return. The prompt of MYSQL is: MySQL >

2. MYSQL connected to remote host.
_Suppose the IP of the remote host is 110.110.110.110, the user name is root, and the password is root. Type the following command:
Mysql-h110.110.110.110-uroot-p root; (Note: there is no space between P and root).

3. Exit MYSQL command:
exit.

2. Modify password

Format: alter user username @host address identified by'New password'

1. Change the root password to new root.
alter user root@localhost identified by 'newroot'
Host address space-time: alter user root identified by'New root'
2. Viewing the Address Method of User Host

mysql -uroot -proot
use mysql;
select user,host from user;

The host column is the host address.

3. Adding new users

Note: Unlike the above, the following commands in the MYSQL environment are followed by a semicolon as the command Terminator

Format: create user's username @ host address identified by password;

1. Increase the password of Tom1 user to tom1, which can be logged in on any host:

create user 'tom1'@'localhost' identified by 'tom1';

2. Quotation marks may be omitted, i.e.

create user tom1@localhost identified by 'tom1';

3. The quotation marks should not be omitted when the host address exists% i.e.

create user tom1@'192.168.1.%' identified by 'tom1';

4.1 Create a database

Note: Connect to Mysql server before creating database

Format: create database database database name

1. Create a database called testdb

   mysql> create database testdb;

4.2 Display database

Format: show databases; (Note: There's an s at the end)

mysql> show databases;

Note: In order to stop scrambling when it is no longer displayed, the default encoding of the database should be modified. The following is illustrated with the utf-8 encoding page as an example:

1. Modify the configuration file of MYSQL: Modify default-character-set=utf-8 in my.ini
2. Code Runtime Modification:
Java code: jdbc: mysql://localhost: 3306/test? UseUnicode = true & characterEncoding = utf-8;

4.3 Delete database

Format: drop database database name;

1. Delete the database named testdb
mysql> drop database testdb;

2. Delete a database that already exists

mysql> drop database testdb;
Query OK, 0 rows affected (0.00 sec)

3. Delete an uncertain database

mysql> drop database testdb;
ERROR 1008 (HY000): Can't drop database 'testdb'; database doesn't exist
//An error occurred and the'testdb'database could not be deleted. The database does not exist.

mysql> drop database if exists testdb;
Query OK, 0 rows affected, 1 warning (0.00 sec)
//Generate a warning that this database does not exist
//View warnings:
mysql> show warnings;
Empty set (0.00 sec)

mysql> create database testdb;
Query OK, 1 row affected (0.00 sec)
mysql> drop database if exists testdb;
//if exists determines whether the database exists, does not exist, and does not produce errors
Query OK, 0 rows affected (0.00 sec)

4.4 Connecting to Database

Format: use database name

1. If the testdb database exists, connect to the database:

mysql> use testdb;
Database changed

The use statement can notify MySQL that the db_name database is used as the default (current) database for subsequent statements. The database remains the default until the end of the paragraph or until a different USE statement is published:

mysql> USE db1;
mysql> SELECT COUNT(*) FROM mytable;   Namely: selects from db1.mytable;
mysql> USE db2;
mysql> SELECT COUNT(*) FROM mytable;   Namely: selects from db2.mytable;

Marking a particular current database with USE statements does not prevent you from accessing tables in other databases. The following example can access author tables from the db1 database and edit tables from the db2 database:

mysql> USE db1;
mysql> SELECT author_name,editor_name FROM author,db2.editor
    ->        WHERE author.editor_id = db2.editor.editor_id;

2. Connecting to other databases
Use commands directly: use other database names.

4.5 Currently selected database

Command: select database();

The select command in MySQL is similar to print or write in other programming languages. You can use it to display a string, a number, the result of a mathematical expression, and so on. Some select commands are as follows:

select version(); // Display mysql version
select now(); // Display the current time
select current_date; // Display year, month and day
select ((4 * 4) / 10 ) + 25; // Calculation

5.1 Create data tables

Format: create table table name (field name 1 type 1,... Field name n type n);

1. Create a table named class:

Field name	Numeric type	Data width	Is it empty?	primary	Self increment	Default value
id	int	4	no	primary key	auto_increment
name	char	20	no
sex	int	4	no			0
degree	double	16	yes

mysql> create table class(
    -> id int(4) not null primary key auto_increment comment 'Primary key',
    -> name varchar(20) not null comment 'Full name',
    -> sex int(4) not null default '0' comment 'Gender',
    -> degree double(16,2) default null comment 'Fraction');
Query OK, 0 rows affected (0.07 sec)

--Check the table for details:
mysql> show full fields from class;
//or
mysql> show full columns from class;
+--------+--------------+-----------------+------+-----+---------+----------------+---------------------------------+---------+
| Field  | Type         | Collation       | Null | Key | Default | Extra          | Privileges                      | Comment |
+--------+--------------+-----------------+------+-----+---------+----------------+---------------------------------+---------+
| id     | int(4)       | NULL            | NO   | PRI | NULL    | auto_increment | select,insert,update,references | Primary key    |
| name   | varchar(20)  | utf8_general_ci | NO   |     | NULL    |                | select,insert,update,references | Full name    |
| sex    | int(4)       | NULL            | NO   |     | 0       |                | select,insert,update,references | Gender    |
| degree | double(16,2) | NULL            | YES  |     | NULL    |                | select,insert,update,references | Fraction    |
+--------+--------------+-----------------+------+-----+---------+----------------+---------------------------------+---------+
4 rows in set (0.01 sec)

5.3 Delete Data Table

Format: drop table table table table name

1. Delete a table named mytable

mysql> drop table mytable;
Query OK, 0 rows affected (0.02 sec)

DROP TABLE is used to cancel one or more tables. You must have DROP permissions for each table. All table data and table definitions will be cancelled, so use this statement carefully!

Note: For a partitioned table, DROP TABLE permanently cancels table definitions, partitions, and all data stored in those partitions. DROP TABLE also cancels the partition definition (.par) file associated with the cancelled table.

2. Delete tables that may not exist
For non-existent tables, IF EXISTS is used to prevent errors. When IF EXISTS is used, a NOTE is generated for each table that does not exist.

mysql> drop table if exists mytable;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings;
+-------+------+---------------------------------+
| Level | Code | Message                         |
+-------+------+---------------------------------+
| Note  | 1051 | Unknown table 'charles.mytable' |
+-------+------+---------------------------------+
1 row in set (0.00 sec)

5.4 Table insertion data

Format: insert into table name (field name 1,... Field name n) values (value 1,... Value n);

1. Insert a record into the table class

mysql> insert into class(name,sex,degree) values('charles','1','80.5');
Query OK, 1 row affected (0.01 sec)

mysql> select * from class;
+----+---------+-----+--------+
| id | name    | sex | degree |
+----+---------+-----+--------+
|  1 | charles |   1 |  80.50 |
+----+---------+-----+--------+
1 row in set (0.00 sec)

2. Insert multiple records

mysql> insert into class(name,sex,degree) values('charles','1','80.5'),('tom','1','80.5');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from class;
+----+---------+-----+--------+
| id | name    | sex | degree |
+----+---------+-----+--------+
|  9 | charles |   1 |  80.50 |
| 10 | tom     |   1 |  80.50 |
+----+---------+-----+--------+
2 rows in set (0.00 sec)

5.5 Query Table Data

1. Query all rows
Format: select field 1,..., field n from table name where expression
Look at all the data in the table class:

mysql> select * from class;
+----+---------+-----+--------+
| id | name    | sex | degree |
+----+---------+-----+--------+
|  1 | charles |   1 |  80.50 |
|  2 | charles |   1 |  80.50 |
|  3 | charles |   1 |  80.50 |
|  4 | charles |   1 |  80.50 |
|  5 | charles |   1 |  80.50 |
|  6 | charles |   1 |  80.50 |
+----+---------+-----+--------+
6 rows in set (0.00 sec)

2. The first few lines of the query
For example, look at the first two rows of data in the table class:

mysql> select * from class limit 2;
+----+---------+-----+--------+
| id | name    | sex | degree |
+----+---------+-----+--------+
|  1 | charles |   1 |  80.50 |
|  2 | charles |   1 |  80.50 |
+----+---------+-----+--------+
2 rows in set (0.00 sec)
select

Usually used in conjunction with where to query more accurate and complex data.

5.6 Delete data from tables

Format: delete from table name where expression

1. Delete the record with id 1 in the table class

mysql> delete from class where id='9';
Query OK, 1 row affected (0.01 sec)

mysql> select * from class;
+----+------+-----+--------+
| id | name | sex | degree |
+----+------+-----+--------+
| 10 | tom  |   1 |  80.50 |
+----+------+-----+--------+
1 row in set (0.00 sec)

5.7 Modify the data in the table

Format:
UPDATE [LOW_PRIORITY] tbl_name SET col_name1=expr1 [, col_name2=expr2 ...] [WHERE where_definition] [ORDER BY ...] [LIMIT row_count]

• The UPDATE grammar can update the columns in the original table rows with new values.
• The SET clause indicates which columns to modify and which values to give.
• The WHERE clause specifies which rows should be updated. If there is no WHERE clause, all rows are updated.
• If the ORDER BY clause is specified, the rows are updated in the specified order.
• The LIMIT clause is used to give a limit to the number of rows that can be updated.

1. A single table update record

mysql> update class set degree = '90.9' where id = 10;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from class;
+----+------+-----+--------+
| id | name | sex | degree |
+----+------+-----+--------+
| 10 | tom  |   1 |  90.90 |
+----+------+-----+--------+
1 row in set (0.00 sec)

2. Single form update multiple records

mysql> update class set degree = '0'
    -> where id < 9
    -> order by id desc
    -> limit 3;
Query OK, 3 rows affected (0.00 sec)
Rows matched: 3  Changed: 3  Warnings: 0

mysql> select * from class;
+----+------+-----+--------+
| id | name | sex | degree |
+----+------+-----+--------+
|  1 | tom1 |   1 |  90.00 |
|  2 | tom2 |   1 |  90.00 |
|  3 | tom3 |   1 |   0.00 |
|  4 | tom4 |   1 |   0.00 |
|  5 | tom5 |   1 |   0.00 |
| 10 | tom  |   1 |  90.90 |
+----+------+-----+--------+
6 rows in set (0.00 sec)

5.8 Adding Fields

See MySQL 5.7 official reference manual for more details

MySQL 5.7 Reference Manual


1. Increase single column
Format: ALTER TABLE tbl_name ADD col_name 1 column_definition [FIRST | AFTER col_name];
[FIRST | AFTER col_name] specifies the location relationship, FIRST denotes the first column, and AFTER col_name denotes the following column;

A field exam_type is added to the table class, type INT(4), default NULL, after the sex column

mysql> ALTER TABLE class
    -> ADD exam_type
    -> INT(4) DEFAULT NULL
    -> COMMENT 'Examination category'
    -> AFTER sex;
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc class;
+-----------+--------------+------+-----+---------+----------------+
| Field     | Type         | Null | Key | Default | Extra          |
+-----------+--------------+------+-----+---------+----------------+
| id        | int(4)       | NO   | PRI | NULL    | auto_increment |
| name      | varchar(20)  | NO   |     | NULL    |                |
| sex       | int(4)       | NO   |     | 0       |                |
| exam_type | int(4)       | YES  |     | NULL    |                |
| degree    | double(16,2) | YES  |     | NULL    |                |
+-----------+--------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

2. Adding multiple columns

mysql> ALTER TABLE class ADD(
    -> col_1 VARCHAR(10) DEFAULT NULL,
    -> col_2 VARCHAR(10) DEFAULT NULL
    -> );
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc class;
+-----------+--------------+------+-----+---------+----------------+
| Field     | Type         | Null | Key | Default | Extra          |
+-----------+--------------+------+-----+---------+----------------+
| id        | int(4)       | NO   | PRI | NULL    | auto_increment |
| name      | varchar(20)  | NO   |     | NULL    |                |
| sex       | int(4)       | NO   |     | 0       |                |
| exam_type | int(4)       | YES  |     | NULL    |                |
| degree    | double(16,2) | YES  |     | NULL    |                |
| col_1     | varchar(10)  | YES  |     | NULL    |                |
| col_2     | varchar(10)  | YES  |     | NULL    |                |
+-----------+--------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)

There are many ways of writing, such as:

ALTER TABLE class ADD COLUMN(
col_1 VARCHAR(10) DEFAULT NULL,
col_2 VARCHAR(10) DEFAULT NULL 
);

ALTER TABLE class 
ADD col_1 VARCHAR(10) DEFAULT NULL,
ADD col_2 VARCHAR(10) DEFAULT NULL;

Note: Location relationships cannot be specified when adding multiple columns.

2. Delete columns
Format: ALTER TABLE tbl_name DROP [COLUMN] col_name 1 [, DROP col_name 2];
- [COLUMN] keywords are optional;
- When deleting multiple columns, we need to use DROP keyword, which can not be used directly and separated.

5.9 Modify Fields

Format:

ALTER TABLE tbl_name
CHANGE [COLUMN] old_col_name new_col_name column_definition
[FIRST|AFTER col_name]

1. Modify the table class column name to name_new

mysql> alter table class
    -> change name name_new varchar(50) not null comment 'Full name'; // Be careful to specify the type
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show full fields from class;
+-----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+----------+
| Field     | Type         | Collation       | Null | Key | Default | Extra | Privileges                      | Comment  |
+-----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+----------+
| id        | int(4)       | NULL            | NO   | PRI | NULL    |       | select,insert,update,references |          |
| name_new  | varchar(50)  | utf8_general_ci | NO   |     | NULL    |       | select,insert,update,references | Full name     |
| sex       | varchar(10)  | utf8_general_ci | YES  |     | NULL    |       | select,insert,update,references |          |
| degree    | double(16,2) | NULL            | YES  |     | NULL    |       | select,insert,update,references | Fraction     |
| exam_type | int(4)       | NULL            | YES  |     | NULL    |       | select,insert,update,references | Examination category |
| remark    | varchar(200) | utf8_general_ci | YES  |     | NULL    |       | select,insert,update,references | Remarks     |
+-----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+----------+
6 rows in set (0.01 sec)

2. Modify table class column sex type to varchar

mysql> alter table class
    -> modify sex varchar(10);
Query OK, 7 rows affected (0.11 sec)
Records: 7  Duplicates: 0  Warnings: 0

mysql> show full fields from class;
+-----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| Field     | Type         | Collation       | Null | Key | Default | Extra | Privileges                      | Comment |
+-----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| id        | int(4)       | NULL            | NO   | PRI | NULL    |       | select,insert,update,references |         |
| name_new  | varchar(50)  | utf8_general_ci | NO   |     | NULL    |       | select,insert,update,references | Full name    |
| sex       | varchar(10)  | utf8_general_ci | YES  |     | NULL    |       | select,insert,update,references |         |
| degree    | double(16,2) | NULL            | YES  |     | NULL    |       | select,insert,update,references | Fraction    |
| exam_type | int(4)       | NULL            | YES  |     | NULL    |       | select,insert,update,references | Examination category  |
+-----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
5 rows in set (0.00 sec)

6.1 Adding Constraints

1. Adding Primary Key Constraints
Format: ALTER TABLE tbl_name ADD [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,... );

• [CONSTRAINT [symbol]] constrain keyword, symbols represent constrained aliases, whether or not, mysql will be created automatically;
• The [index_type] index type contains {BTREE | HASH} and only BTREE is used when the storage engine is InnoDB, and the default value is BTREE.
  Adding primary key constraints to id columns in table class

mysql> ALTER TABLE class
    -> add CONSTRAINT pk_id PRIMARY KEY
    -> USING BTREE (id);
Query OK, 0 rows affected (0.10 sec)
Records: 0  Duplicates: 0  Warnings: 0
// View constraints:
mysql> select constraint_name,table_schema,table_name,column_name from information_schema.key_column_usage
    -> where table_name = 'class';
+-----------------+--------------+------------+-------------+
| constraint_name | table_schema | table_name | column_name |
+-----------------+--------------+------------+-------------+
| PRIMARY         | charles      | class      | id          |
+-----------------+--------------+------------+-------------+
1 row in set (0.00 sec)
//Note: constraint_name is not pk_id, indicating that symbol s in the command are not in effect, and I don't know why.
//Or:
mysql> show keys from class;
//Or:
mysql> show index from class;

If: ERROR 1068 (42000): Multiple primary key definition, indicating that the definition of the primary key is repeated, the id column already has the primary key, so we need to delete the primary key first. Delete method reference:
Delete the primary key in MySQL
Change from: https://blog.csdn.net/LanTingShuXu/article/details/70215063

2. Adding Unique Constraints
Format:

ALTER TABLE tbl_name ADD [CONSTRAINT [symbol]] UNIQUE [INDEX|KEY] [index_name] [index_type] (index_col_name,...);

• [INDEX|KEY] Describes whether it is INDEX or KEY. Reference to the difference between INDEX and KEY: The Difference between key and index in Database Operation
  (from: https://www.cnblogs.com/654321cc/p/7762943.html)
• [index_name] index name seems to be no different from [CONSTRAINT [symbol];
• [index_type] index type, including {BTREE | HASH},
• This part of the narrative reference: mysql index creation, modification and deletion
  (from: https://blog.csdn.net/yue7603835/article/details/54925374)

1) Add unique constraints to the table class column name

mysql> ALTER TABLE class
    -> ADD UNIQUE KEY uk_name USING BTREE (name);
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> select constraint_name,table_schema,table_name,column_name from information_schema.key_column_usage
    -> where table_name = 'class';
+-----------------+--------------+------------+-------------+
| constraint_name | table_schema | table_name | column_name |
+-----------------+--------------+------------+-------------+
| PRIMARY         | charles      | class      | id          |
| uk_name         | charles      | class      | name        |
+-----------------+--------------+------------+-------------+
2 rows in set (0.00 sec)
//The constraint_name of this constraint takes effect and is used in the command constraint uk_name The effect is the same.
//At the same time, index_name has a high priority when used.

2) Attempt to insert duplicate name tom

mysql> select * from class;
+----+------+-----+-----------+--------+
| id | name | sex | exam_type | degree |
+----+------+-----+-----------+--------+
|  1 | tom1 |   1 |      NULL |  90.00 |
|  2 | tom2 |   1 |      NULL |  90.00 |
|  3 | tom3 |   1 |      NULL |   0.00 |
|  4 | tom4 |   1 |      NULL |   0.00 |
|  5 | tom5 |   1 |      NULL |   0.00 |
|  6 | tom6 |   0 |      NULL |   NULL |
| 10 | tom  |   1 |      NULL |  90.90 |
+----+------+-----+-----------+--------+
7 rows in set (0.00 sec)
mysql> insert into class(id, name) values(7,'tom');
ERROR 1062 (23000): Duplicate entry 'tom' for key 'uk_name' 
// Repeat input for constraint'uk_name', cannot insert

3) Delete unique constraints

mysql> alter table class drop key uk_name;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show keys from class;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| class |          0 | PRIMARY  |            1 | id          | A         |           7 |     NULL | NULL   |      | BTREE      |         |               |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

6.2 Adding Index

1. Indexing
Format:

  General index
ALTER TABLE tbl_name
ADD {INDEX|KEY} [index_name]
(key_part,...) [index_option] ...

  //Full-text index
ALTER TABLE tbl_name
ADD FULLTEXT [INDEX|KEY] [index_name]
(key_part,...) [index_option] ...

  //Spatial index
ALTER TABLE tbl_name
ADD SPATIAL [INDEX|KEY] [index_name]
(key_part,...) [index_option] ...

key_part:
    col_name [(length)] [ASC | DESC]

index_type:
    USING {BTREE | HASH}

index_option:
    KEY_BLOCK_SIZE [=] value
  | index_type
  | WITH PARSER parser_name
  | COMMENT 'string'

• The format refers to the official Manual of the corresponding version.
• [] means nonessential, {} means multiple choices.
• Reference to the meanings of key_part and index_type and index_option: MySQL Advanced Syntax
  (from: https://blog.csdn.net/rongxiaojun1989/article/details/77731662)
• The index is simple for comparison. Comparison of primary key, general index, unique index and full-text index
  (from: https://www.cnblogs.com/xuzhengzong/p/7680464.html)

1) Add a common index to the table class column name

mysql> alter table class
    -> add index name_index (name);
Query OK, 0 rows affected (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show index from class;
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| class |          0 | PRIMARY    |            1 | id          | A         |           7 |     NULL | NULL   |      | BTREE      |         |               |
| class |          1 | name_index |            1 | name        | A         |           7 |     NULL | NULL   |      | BTREE      |         |               |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)

2) Add a common index to the class column remark of the table

Add column remark: 
mysql> alter table class
    -> add remark varchar(200) default null comment 'Remarks';

//Add full-text index:
mysql> alter table class
    -> add fulltext remark_full (remark);
Query OK, 0 rows affected, 1 warning (0.34 sec)
Records: 0  Duplicates: 0  Warnings: 1

mysql> show index from class;
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name    | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| class |          0 | PRIMARY     |            1 | id          | A         |           7 |     NULL | NULL   |      | BTREE      |         |               |
| class |          1 | name_index  |            1 | name        | A         |           7 |     NULL | NULL   |      | BTREE      |         |               |
| class |          1 | remark_full |            1 | remark      | NULL      |           7 |     NULL | NULL   | YES  | FULLTEXT   |         |               |
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)

3) Delete index

mysql> alter table class
    -> drop index name_index,
    -> drop index remark_full;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show index from class;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| class |          0 | PRIMARY  |            1 | id          | A         |           7 |     NULL | NULL   |      | BTREE      |         |               |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)