表与表之间的数据记录有关系(relationship)。现实世界中的各种实体以及实体之间的各种联系均用关系模型来表示。 四种:一对一关联、一对多关联、多对多关联、自我引用 2.3一对一关联(one-to-one) 常见实例场景: 客户表和订单表 , 分类表和商品表 , 部门表和员工表 。
flask import Flask from flask.ext.sqlalchemy import SQLAlchemy app=Flask(__name__) db=SQLAlchemy(app) 一对多...: 一对一需要设置relationship中的uselist=Flase,其他数据库操作一样。...多对多: 创建表: tags=db.Table('tags',db.Column('student_id',db.Integer,db.ForeignKey('student.id')),db...
Dear Peter, After you recommendations, I found some tutorials about one-to-many relationship and I implemented a solution that seems working. Could you please have a look on my script and give me some feedback if it is something optimal for my application. Thank you. ...
An identifying relationship is one where the child table cannot be uniquely identified without its parent. Typically this occurs where an intermediary table is created to resolve a many-to-many relationship. In such cases, the primary key is usually a composite key made up of the primary keys ...
Description:Cannot delete the relationship between two tables.How to repeat:In the EER diagram view, create a one to many relationship between two tables. Arrange the tables so that the crow's foot notation relationship line is not stepped i.e it is a straight line joining the two tables. ...
CREATE TABLE stu_info ( id INT PRIMARY KEY AUTO_INCREMENT, -- 学生ID,主键自增长 name VARCHAR(50) NOT NULL, -- 学生姓名,不允许为空 gender ENUM('男', '女') DEFAULT '男', -- 学生性别,枚举类型,默认为男 age INT DEFAULT 18, -- 学生年龄,默认为18岁 ...
CREATETABLEnode(idINTPRIMARYKEY,nameVARCHAR(50));CREATETABLErelationship(ancestor_idINT,descendant_idINT,FOREIGNKEY(ancestor_id)REFERENCESnode(id),FOREIGNKEY(descendant_id)REFERENCESnode(id)); 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
one-to-one– It is the type of relationship where one record is connected to a single record in another table. one-to-many– When multiple records in one table are connected to one record in another table, this is known as a one-to-many relationship. ...
The second table is for vip level and expiration. A user can have multiple level and different expiration date for every one of them. What I'm trying to accomplish is to return only the highest valid level, not expired. CREATE TABLE `users` ( `id` int(11) NOT NULL AUTO_INCREMENT, `...
App has users and users can create projects while projects can have multiple keywords. So users are in one-to-many relationship with projects and projects are in many-to-many relationships with tags. So having table `users` I suppose projects table should be `users_projects`. But what ...