Among them, CREATE, DROP and ALTER are statements that implement the data definition function.

The SQL language set mainly consists of four parts: data definition, data query, data manipulation, and data control.

1. Data definition language is used to define the structure of data, such as creating, modifying or deleting database objects. The corresponding statements are CREATE, ALTER and DROP;

2. Data query language Used for retrieval, use SELECT statement to retrieve data;

3. Data manipulation language is used to modify data. Modifying data includes insert, update and delete. The corresponding statements are INSERT, UPDATE and DELETE;

4. The data control language is used to define the permissions of database users. The GRANT statement is used to grant permissions, the REVOKE statement is used to revoke permissions, and so on.

Extended information

Detailed introduction to the four components of Structured Query Language SQL:

1. Data Definition Language (DDL)

Data Definition Language (DDL) is a language that is responsible for the definition of data structures and database objects in the SQL language.

Used to define the three-level structure of the database, including external schema, conceptual schema, internal schema and their mutual images, and define data integrity, security control and other constraints. DDL does not require commit.

2. Data Manipulation Language (DML)

Data Manipulation Language DML (Data Manipulation Language) allows users to perform basic operations on the database. Provided by DBMS, used by users or programmers to operate data in the database.

DML is divided into two categories: interactive DML and embedded DML. According to the level of language, DML can be divided into two types: procedural DML and non-procedural DML. DML requires commit.

3. Data Query Language (DQL)

Data Query Language DQL (Data Query Language) mainly includes the query of data table records.

4. Data Control Language (DCL)

Data Control Language (Data Control Language) is a statement used to set or change database user or role permissions, including basic tables and views Authorization, description of integrity rules, transaction control, etc.

Baidu Encyclopedia-Structured Query Language