A must-read for learning MySQL! Detailed explanation of the basic knowledge of SQL statements

MySQL is an open source relational database management system that is widely used in web application development and data storage. Learning MySQL's SQL language is very necessary for data managers and developers. SQL language is the core part of MySQL, so before learning MySQL, you need to have a full understanding of SQL language. This article aims to explain the basic knowledge of SQL statements to you in detail, so that you can understand SQL statements step by step.

SQL is the abbreviation of Structured Query Language, which is used to store, operate and retrieve data in relational databases. It has a clear syntax structure containing different commands and keywords. The following is a brief explanation of the basic elements of SQL statements:

1. Database operation statements

In MySQL, database creation, switching, deletion and backup are completed through database operation statements. Wait for operations. The following are some commonly used database operation statements:

• Create a new database

CREATE DATABASE database_name;

• Switch to the specified database

USE database_name;

• Delete a specified database

DROP DATABASE database_name;

• Backup database

To back up the entire database, you can use the mysqldump command, such as the following command to back up the current database:

mysqldump -u user_name -p database_name > backup.sql

2. Table operation statement

The table is the most basic component of the relational database. The table is composed of rows and columns. In MySQL, operations such as creating, modifying, and deleting tables are completed through table operation statements. Commonly used table operation statements are as follows:

• Create a new table

CREATE TABLE table_name (column1 datatype, column2 datatype,....);

• Modify table structure

ALTER TABLE table_name ADD column_name datatype;

ALTER TABLE table_name DROP COLUMN column_name;

ALTER TABLE table_name MODIFY column_name datatype;

• Delete the specified table

DROP TABLE table_name;

3. Data operation statement

In the database , we need to add, delete and update data. The following are some commonly used data manipulation statements:

• Insert data into the table

INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);

• Delete the specified data in the table

DELETE FROM table_name WHERE condition;

• Update table Data in

UPDATE table_name SET column_name1 = value1, column_name2 = value2 WHERE condition;

4. Query statement

The query statement is a SQL command The most important part is mainly used to retrieve data from the table. The following are commonly used query statements:

• Query all columns in the table

SELECT * FROM table_name;

• Query the specified columns in the table Data

SELECT column1, column2, ... FROM table_name;

• Query and filter data according to conditions

SELECT column1, column2, ... FROM table_name WHERE condition;

• Arrange the query results in ascending or descending order

SELECT column1, column2, ... FROM table_name ORDER BY column1 DESC;

5. Join query statement

Join query is used to retrieve related data between multiple tables. The following are some commonly used join query statements:

• Inner join query

SELECT column1, column2, ... FROM table1 INNER JOIN table2 ON table1.column_name = table2. column_name;

• Left join query

SELECT column1, column2, ... FROM table1 LEFT JOIN table2 ON table1.column_name = table2.column_name;

• Right join query

SELECT column1, column2, ... FROM table1 RIGHT JOIN table2 ON table1.column_name = table2.column_name;

The above is the basic knowledge of SQL statements In summary. Learning the SQL language is not as difficult as imagined. You will become more proficient in it as you slowly explore it in practice. If you need to learn the SQL language in more depth, you can deepen your understanding by consulting MySQL official documentation or referring to some online video tutorials. Whether you are a developer or a data administrator, understanding the SQL language will allow you to manage and operate MySQL databases more efficiently.

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