What statements are added to MySQL

mysql What is the added statement

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Add statement has ：1、CREATE DATABASE sentence , Used to add database , grammar “CREATE DATABASE Database name ;”;2、CREATE TABLE sentence , Used to add data table , grammar “CREATE TABLE Table name ( Name type );”;3、ALTER TABLE sentence , You can add fields to the data table , grammar “ALTER TABLE Table name ADD Field name type ;”;4、INSERT sentence , You can add data to a field .

The operating environment of this tutorial ：windows7 System 、mysql8 edition 、Dell G3 The computer .

1、MySQL Add database （CREATE DATABASE sentence ）

stay MySQL in , have access to CREATE DATABASE Statement create database , The basic syntax is as follows ：

CREATE DATABASE [IF NOT EXISTS]  Database name [CHARACTER SET  Character set name ] [COLLATE  Proofreading rule name ];

• IF NOT EXISTS： Judge before creating the database , The operation can only be performed if the database does not currently exist . This option can be used to avoid the error of repeatedly creating the existing database .

• CHARACTER SET： Specify the character set of the database . The purpose of specifying the character set is to avoid garbled data stored in the database . If the character set is not specified when creating the database , Then use the system's default character set .

• COLLATE： Specifies the default collation rules for the character set .

MySQL Character set for （CHARACTER） And proofreading rules （COLLATION） It's two different concepts . The character set is used to define MySQL How to store strings , Proofing rules define how strings are compared . We'll explain it separately later MySQL The character set and proofreading rules of .

Example ： Create a file called test_db The database of

CREATE DATABASE test_db;

View or display databases

SHOW DATABASES;

2、MySQL Add data sheet （CREATE TABLE sentence ）

stay MySQL in , have access to CREATE TABLE Statement create table . Its grammatical form is ：

CREATE TABLE < Table name > ([ Table definition options ])[ Table options ][ Partition options ]);

among ,[ Table definition options ] The format is ：

< Name 1> < type 1> [,…] < Name n> < type n>

CREATE TABLE More command syntax , It is mainly created and defined by the table （create-definition）、 Table options （table-options） And partition options （partition-options） Made up of .

Tips ： Use CREATE TABLE Create table time , The following information must be specified ：

• The name of the table to be created is not case sensitive , Out of commission SQL Keywords in language , Such as DROP、ALTER、INSERT etc. .

• Each column in the data table （ Field ） Name and data type of , If you create multiple columns , Separate them with commas .

Example ： Create a table in the specified database

notes ： Data table belongs to database , Before creating the data table , Statement expected “USE< database >” Specify the database in which the operation is performed , If no database is selected , Will throw No database selected Error of .

Select the database to create the table test_db, establish tb_emp1 Data sheet ：

CREATE TABLE tb_emp1(id INT(11),name VARCHAR(25),deptId INT(11),salary FLOAT);

After statement execution , You create a file named tb_emp1 Data sheet for , Use SHOW TABLES; Statement to check whether the data table is created successfully

3、MySQL Add fields to the data table （ALTER TABLE sentence ）

stay MySQL Can be used in ALTER TABLE Statement to change the structure of the original table , For example, add or delete columns 、 Change the original column type 、 Rename columns or tables, etc .

A complete field includes the field name 、 Data types and constraints .MySQL The syntax format for adding fields is as follows ：

ALTER TABLE < Table name > ADD < new field name >< data type >[ constraint condition ];

The syntax of the format is as follows ：

• < Table name > For the name of the data table ;

• < new field name > For the name of the field to be added ;

• < data type > The data type that can store data for the field to be added ;

• [ constraint condition ] It's optional , Used to constrain the added fields .

This syntax format defaults to the last position in the table （ After the last column ） Add new fields .

Example ： stay tb_emp1 Add fields to the data table

Use DESC see tb_emp1 Table structure

DESC tb_emp1;

Use ALTER TABLE Add a INT Type field age

ALTER TABLE tb_emp1 ADD age INT(4);

4、MySQL Add data （INSERT sentence ）

After the database and table are created successfully , You need to insert data into the tables in the database . stay MySQL Can be used in INSERT Statement to insert one or more rows of tuple data into an existing table in the database .

INSERT There are two grammatical forms of sentences , Namely INSERT…VALUES Statement and INSERT…SET sentence .

1)、 INSERT…VALUES sentence

INSERT VALUES The grammar format of is ：

INSERT INTO < Table name > [ < Name 1> [ , … < Name n>] ]VALUES ( value 1) [… , ( value n) ];

The grammar is as follows .

• < Table name >： Specifies the name of the table being manipulated .

• < Name >： Specify the name of the column to insert the data . If you insert data into all the columns in the table , Then all column names can be omitted , Direct adoption INSERT< Table name >VALUES(…) that will do .

• VALUES or VALUE Clause ： This clause contains the list of data to insert . The order of the data in the data list corresponds to the order of the columns .

2)、INSERT…SET sentence

The grammar format is ：

INSERT INTO < Table name >SET < Name 1> = < value 1>,        < Name 2> = < value 2>,        …

This statement is used to specify the corresponding column values directly to some columns in the table , The column name of the data to be inserted is in SET Clause ,col_name For the specified column name , After the equal sign is the specified data , And for unspecified Columns , The column value is specified as the default value for that column .

notes ： When using a single INSERT When a statement inserts multiple rows of data , Just enclose each row of data in parentheses .

Example ： Add values to all fields in the table

stay test_db Create a course information table in the database tb_courses, Include course number course_id、 Course name course_name、 course credit course_grade And course notes course_info

CREATE TABLE tb_courses(course_id INT NOT NULL AUTO_INCREMENT,course_name CHAR(40) NOT NULL,course_grade FLOAT NOT NULL,course_info CHAR(100) NULL,PRIMARY KEY(course_id));

• stay tb_courses Insert a new record into the table ,course_id The value is 1,course_name The value is “Network”,course_grade The value is 3,info The value is “Computer Network”

Before performing the insert operation , see tb_courses surface

SELECT * FROM tb_courses;

The query result shows that the content of the current table is empty , No data , Next, perform the operation of inserting data

INSERT INTO tb_courses(course_id,course_name,course_grade,course_info)VALUES(1,'Network',3,'Computer Network');

You can see that the record is inserted successfully . When inserting data , It specifies tb_courses All fields of the table , Therefore, a new value will be inserted for each field .

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