Let's talk about what DDL, DML, DQL and DCL are in SQL statements

The core language of the database is the SQL language. What are DDL, DML, DQL, and DCL?Let's talk about these four concepts.

• • • I. DDL Statement
    • II. DML Statement
    • Three, DQL Statement
    • Four. DCL Statement

I. DDL Statement

DDL (Data Definition Language) statement: Data Definition Language, mainly to define/change the table structure, data type, link between tables and other operations.Commonly used statement keywords are CREATE, DROP, ALTER, etc.

The template is as follows:

CREATE TABLE table name(column name 1 data type,column name 2 data type,column name 3 data type,...)ALTER TABLE tablename;eg: ALTER TABLE table name ADD column name data type; (add a column)ALTER TABLE table name CHANGE column name new column name new data type; (modify column name)ALTER TABLE table name DROP column name;DROP TABLE table name;DROP DATABASE database name;

Second, DML statement

DML (Data Manipulation Language) statement: Data Manipulation Language, mainly for adding, deleting and modifying data.Commonly used statement keywords are INSERT, UPDATE, DELETE, etc.

The main differences between DDL statements and DML statements:

DDL

DML

Name

Data Definition Language

Data manipulation language

Difference

Create, delete, modify objects in database

Only operate on the data within the table (does not involve the definition of the table, the modification of the structure, or other objects)

The template is as follows:

INSERT INTO table name (field1,field2,...) values ​​(some value,some value,...),(some value,some value,...);UPDATE tablename SET columnname=new value WHERE qualification;DELETE FROM table name WHERE qualification;

Third, DQL statement

DQL (Data Query Language) statement: Data Query Language, mainly for querying data.Common keywords are SELECT, FROM, WHERE, etc.

The template is as follows:

SELECT column name FROM table name WHERE qualification;

Fourth, DCL statement

DCL (Data Control Language) statement: Data Control Language, mainly used to set/change database user permissions.Common keywords are GRANT, REVOKE, etc.
DCL statements are rarely used by ordinary people.

The template is as follows:

GRANT (Grant)REVOKE (revoke permission)

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