zoukankan      html  css  js  c++  java
  • mysql 外键

    1. sql新建
    CREATE DATABASE IF NOT EXISTS dbdemo;
    
    USE dbdemo;
    
    CREATE TABLE categories(
       cat_id int not null auto_increment primary key,
       cat_name varchar(255) not null,
       cat_description text
    ) ENGINE=InnoDB;
    
    CREATE TABLE products(
       prd_id int not null auto_increment primary key,
       prd_name varchar(355) not null,
       prd_price decimal,
       cat_id int not null,
       FOREIGN KEY fk_cat(cat_id)
       REFERENCES categories(cat_id)
       ON UPDATE CASCADE
       ON DELETE RESTRICT
    )ENGINE=InnoDB;
    
    
    
    1. sql修改
    USE dbdemo;
    
    CREATE TABLE vendors(
        vdr_id int not null auto_increment primary key,
        vdr_name varchar(255)
    )ENGINE=InnoDB;
    
    
    ALTER TABLE products 
    ADD COLUMN vdr_id int not null AFTER cat_id;
    
    
    ALTER TABLE products
    ADD FOREIGN KEY fk_vendor(vdr_id)
    REFERENCES vendors(vdr_id)
    ON DELETE NO ACTION
    ON UPDATE CASCADE;
    
    
    1. ORM新建
    class UserGroup(models.Model):
        uid = models.Auto(primary_key=True)
        title=models.CharField(max_length=32,unique=True)
    
    class UserInfo(models.Model):
        username=models.CharField(max_length=32)
        user_group = models.ForeignKey("UserGroup", to_field="uid", default=1, on_delete=models.CASCADE)
    
    
    
  • 相关阅读:
    idea快捷方式2
    idea快捷方式1
    小程序数组倒序
    小程序列表倒计时 wxs 实现
    cnpm
    小程序的空判断
    小程序正则写法
    Sphinx中文入门指南——新手可先看此文
    sphinx –rotate机制详解
    sphinx数据文件简析
  • 原文地址:https://www.cnblogs.com/amize/p/14102653.html
Copyright © 2011-2022 走看看