关系表在sqlite上的android [英] relationship tables in sqlite on android

问题描述

你可以帮助我了解sqlite中两个表之间的关系。

我插入，删除和更新步骤，但是我必须支持两个表之间的关系。我想

所有的代码步骤，之前做的都会改变我是对吗？
你有任何链接或示例来解释关系之后的表关系和任何活动吗？

解决方案

两个表格，您可以使用外键。外键是关系表中与另一个表的候选键匹配的字段。

在 SQLite外键约束可以按以下方式添加：

edit ::
你可以像下面这样设计item_order表：

  CREATE TABLE customer（
 id INTEGER，
 firstName TEXT，
 middleName TEXT，
 lastName TEXT，
 address TEXT，
 contactNum TEXT 
）; 
 
 CREATE TABLE item（
 id INTEGER，
 name TEXT，
 description TEXT 
）; 
 
 CREATE TABLE order（
 id INTEGER，
 customerID INTEGER，
 date TEXT，
 FOREIGN KEY（customerId）REFERENCES customer（id）
）; 
 
 CREATE TABLE item_order（
 id INTEGER，
 orderID INTEGER，
 itemId INTEGER，
 quantity INTEGER，
 FOREIGN KEY（orderId）REFERENCES order（Id），
 FOREIGN KEY（itemId）REFERENCES item（Id）
）; 
  

Can you help me about relationship between two tables in sqlite.

I do insert,delete and update steps but I have to support relationship between two tables now. I guess
all of code steps which are done before will be changed Am I right? Have you got any link or example which explains tables relationships and any activities after relationship?

解决方案

To establish relationship between two tables, you can use Foreign keys. A foreign key is a field in a relational table that matches a Candidate Key of another table.

For example, say we have two tables, a CUSTOMER table that includes all customer data, and an ORDER table that includes all customer orders. The intention here is that all orders must be associated with a customer that is already in the CUSTOMER table. To do this, we will place a foreign key in the ORDER table and have it relate to the primary key of the CUSTOMER table.

In SQLite Foreign Key Constraints can be added in following way ::

edit:: you can design item_order table like ::

CREATE TABLE customer(
         id INTEGER,
         firstName TEXT,
         middleName TEXT,
         lastName   TEXT,
         address TEXT,
         contactNum TEXT
);

 CREATE TABLE item(
        id INTEGER,
        name TEXT,
        description TEXT
 );

 CREATE TABLE order(
        id INTEGER,
        customerID INTEGER,
        date TEXT,
        FOREIGN KEY(customerId) REFERENCES customer(id)
 );

 CREATE TABLE item_order(
        id INTEGER,
        orderID INTEGER,
        itemId  INTEGER,
        quantity INTEGER,
        FOREIGN KEY(orderId) REFERENCES order(Id),
        FOREIGN KEY(itemId) REFERENCES item(Id)
 );

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