mysql day2

sql语句执行顺序
FROM/JOIN → WHERE → GROUP BY → HAVING → 窗口函数(OVER) → SELECT → DISTINCT → ORDER BY → LIMIT
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简单的用法

1. 数据库操作

• 创建数据库 create database db1;
• 使用数据库use db1;

2.数据定义DDL:create,drop,alter

• 创建表
  create table t1 (id int primary key, name varchar(20)...);
• 修改表
  alter table t1 add column id int;
alter table t1 modify column id varchar(20);
alter table t1 drop column name;
alter table t1 rename to t2;
• 查看表
  desc t1;-- 查看表结构
show tables;-- 查看所有表

3.数据操纵DML:insert，update

• 插入数据

--插入多条数据
INSERT INTO user (name, age, email) VALUES 
  ('张三', 25, 'zhangsan@test.com'),
  ('李四', 30, 'lisi@test.com'); 

--插入全部信息
INSERT INTO user VALUES (3, '王五', 28, 'wangwu@test.com', '2026-01-26 10:00:00');

• 修改数据
  UPDATE user SET age = 26, email = 'zhangsan_new@test.com' WHERE id = 1;

• 删除数据
  DELETE FROM user WHERE id = 3;
truncate table t1; -- 清空表及相关信息