SQL language basics

When I watched the database video, I once talked about the content of the SQL language. I sorted it out below

Standard SQL contains nine statements.

 

Data Query	Select
Data Definition	Create, drop, alter
Data manipulation	Insert, update, delete
Data Control	Grant, revoke

 

The SQL language can be divided into four categories:

Category	Function	Example
Data Definition Language (DDL)	Defines the data structure and creates, modifies, and deletes database objects.	Create Table: Create a database table Drop index: Delete the table index. Alter table: Add a table column, redefine the table column, and change the storage allocation.
Data manipulation language (DML)	Allows you to insert or update data in the database.	Insert: add data rows to the table Select: Retrieves data rows. Delete: delete data rows. Update: Change Data
Data Control Language (DCL)	Used to specify various permissions of database users	GRANT: grant permissions or roles to users or other roles Revoke: revoke permissions from a user or database role
Database Transaction Control Language	To ensure database integrity	Commit work: Write the changes made by the current firm to the disk. Rollback: invalidate all changes since the last submission

In addition, pay special attention to code specifications when writing SQL statements.

Basic SQL statement Syntax:

1. Each statement must end with a semicolon.

2. Free writing. You can use SQL statements to write a single row (long rows are not recommended) or separate them into several rows.

3. It is case-insensitive. keywords, table names, and column names can be case-insensitive, but the content of columns is case-sensitive.