sql first understanding

sql is a standard computer language used to access and process databases.

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SQL refers to structured query language, an ANSI standard computer language that enables us to access databases.

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sql can do:

SQL 面向数据库执行查询
SQL 可从数据库取回数据
SQL 可在数据库中插入新的记录
SQL 可更新数据库中的数据
SQL 可从数据库删除记录
SQL 可创建新数据库
SQL 可在数据库中创建新表
SQL 可在数据库中创建存储过程
SQL 可在数据库中创建视图
SQL 可以设置表、存储过程和视图的权限

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SQL is not case sensitive, and a semicolon is used to separate each SQL statement in the database, so that more than one statement can be executed in the same request to the server.

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SQL is divided into two parts: Data Manipulation Language (DML) and Data Definition Language (DDL).
The query and update instructions form the DML part of SQL:

SELECT - 从数据库表中获取数据
UPDATE - 更新数据库表中的数据
DELETE - 从数据库表中删除数据
INSERT INTO - 向数据库表中插入数据

The data definition language (DDL) part of SQL gives us the ability to create or delete the
most important DDL statements in table SQL:

CREATE DATABASE - 创建新数据库
ALTER DATABASE - 修改数据库
CREATE TABLE - 创建新表
ALTER TABLE - 变更（改变）数据库表
DROP TABLE - 删除表
CREATE INDEX - 创建索引（搜索键）
DROP INDEX - 删除索引