SQL语言: 基本操作

偶尔有点困Z2024-03-29 19:07

DDL(数据定义)

库

创建数据库 CREATE DATABASE database_name;
删除数据库 DROP DATABASE database_name;
选择数据库 USE database_name;

表

创建表格 CREATE TABLE table_name( column1 datatype, column2 datatype, ... );
删除表格 DROP TABLE table_name;
修改表格

        ALTER TABLE table_name ADD column_name datatype; -- 添加列

        ALTER TABLE table_name MODIFY column_name datatype; -- 修改列

        ALTER TABLE table_name DROP column_name; -- 删除列

约束

设置主键
ALTER TABLE table_name ADD CONSTRAINT constraint_name 
PRIMARY KEY (column1, column2, ...);

设置外键
ALTER TABLE table_name ADD CONSTRAINT constraint_name 
FOREIGN KEY (column) REFERENCES other_table(column);

索引

创建索引 CREATE INDEX index_name ON table_name (column1, column2, ...);
删除索引 DROP INDEX index_name ON table_name;

DML(数据操纵)

查询数据

SELECT column1, column2, ... FROM table_name WHERE condition;
ORDER BY xx --升序
ORDER BY xx DESC --降序

插入数据

INSERT INTO table_name (column1, column2, ...) VALUES (value1, value2, ...);

更新数据

UPDATE table_name SET column1 = value1, column2 = value2, ... WHERE condition;

删除数据

DELETE FROM table_name WHERE condition;

DCL(数据控制)

创建用户

CREATE USER 'username'@'host' IDENTIFIED BY 'password';

删除用户

DROP USER 'username'@'host';

修改密码

SET PASSWORD FOR 'username'@'host' = 'new_password';

刷新权限

FLUSH PRIVILEGES;

授予权限

GRANT privileges ON database_name.table_name TO 'user'@'host';

收回权限

REVOKE privileges ON database_name.table_name FROM 'user'@'host';