An in-depth discussion of the meaning and functions of SQL

In-depth analysis of the meaning and function of SQL

Introduction
With the rapid development of modern information technology, the generation and storage of massive data has become a norm. To process these massive data, we need an efficient, powerful, and flexible tool. Structured Query Language (SQL), as a language widely used in database management systems, has undoubtedly become such a tool. This article will deeply analyze the meaning and function of SQL and provide specific code examples.

1. The definition and characteristics of SQL
SQL, the full name of Structured Query Language, is a computer language used to manage, operate and query relational databases. Compared with other programming languages, SQL has the following characteristics:

1. Declarative language: SQL is a declarative language. Users only need to describe the required data without paying attention to the specific implementation. step.
2. Database operation language: SQL allows users to perform various operations on the database, including creation, query, modification and deletion, etc.
3. For relational databases: SQL is mainly suitable for relational database management systems (RDBMS), such as MySQL, Oracle, SQL Server, etc.
4. Easy to learn: The syntax of SQL is relatively simple and easy to be understood and learned.

2. The role of SQL

1. Data definition (DDL): DDL is used to define various objects in the database, such as tables (CREATE TABLE), View (CREATE VIEW), etc. Below is a sample code to create a table:

   CREATE TABLE students (
     id INT PRIMARY KEY,
     name VARCHAR(50),
     age INT,
     gender CHAR(1)
   );

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2. Data Query (DQL): DQL is used to obtain the required data from the database. By using the SELECT statement, specified data can be retrieved from the database. The following is a simple SELECT statement example:

   SELECT * FROM students WHERE age > 20;

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3. Data operation (DML): DML is used to operate data in the database, including inserting data, updating data, deleting data, etc. The following is an example of inserting data:

   INSERT INTO students (id, name, age, gender) VALUES (1, "Tom", 22, "M");

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4. Data Control (DCL): DCL is used to control and securely manage data in the database, including granting user permissions, revoking user permissions, etc. . The following is an example of granting permissions:

   GRANT SELECT ON students TO user1;

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5. Transaction Control (TCL): TCL is used to manage and control operations that have been performed to ensure the integrity and consistency of the database. The following is a sample code for a transaction:

   START TRANSACTION;
   UPDATE students SET age = 23 WHERE id = 1;
   COMMIT;

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3. SQL code examples
Next, we will further illustrate the role of SQL through several specific SQL code examples. Suppose we have a table called "employees" with the following fields: id, name, age, gender, salary.

1. Query the names and salaries of all employees:

   SELECT name, salary FROM employees;

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2. Find the names and salaries of employees with a salary greater than 5,000:

   SELECT name, salary FROM employees WHERE salary > 5000;

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3. Increase the salary of all male employees by 10%:

   UPDATE employees SET salary = salary * 1.1 WHERE gender = 'M';

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4. Add a new employee:

   INSERT INTO employees (id, name, age, gender, salary) VALUES (1001, 'Alice', 30, 'F', 7000);

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5. Remove age Employees greater than 60 years old:

   DELETE FROM employees WHERE age > 60;

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Conclusion
As a language used to manage, operate and query relational databases, SQL is easy to learn, efficient and powerful. By using SQL, we can easily perform various operations and queries on the database. This article deeply analyzes the meaning and function of SQL and gives specific code examples, hoping to help readers better understand and apply SQL.

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