在MySQL中创建表之间的一对一和一对多关系
我正在准备考试,我决定做一些我自己编的例题,但我有一个特别的问题。关系。我已经在SQL上碰头3-4个小时了,但进展甚微。我有两个表,我想在其中创建一对一和一对多关系在MySQL中创建表之间的一对一和一对多关系,mysql,sql,database-design,foreign-key-relationship,Mysql,Sql,Database Design,Foreign Key Relationship,我正在准备考试,我决定做一些我自己编的例题,但我有一个特别的问题。关系。我已经在SQL上碰头3-4个小时了,但进展甚微。我有两个表,我想在其中创建一对一和一对多关系 CREATE TABLE article ( price INT(30) NOT NULL, published_on DATE NOT NULL ); CREATE TABLE tag( descption VARCHAR(30) NOT NULL, priority INT(30) NOT NU
CREATE TABLE article (
price INT(30) NOT NULL,
published_on DATE NOT NULL
);
CREATE TABLE tag(
descption VARCHAR(30) NOT NULL,
priority INT(30) NOT NULL
);
CREATE TABLE category(
date_created_on DATE NOT NULL,
name VARCHAR(30) NOT NULL
);
INSERT INTO article VALUES (10.0, "2001-01-01", 0);
INSERT INTO article VALUES (20.0, "1992-05-08", 0);
INSERT INTO tag VALUES ("wtf", 1, 1);
INSERT INTO tag VALUES ("is this", 2, 2);
ALTER TABLE article ADD article_id INT(30) NOT NULL;
ALTER TABLE article ADD PRIMARY KEY(article_id);
ALTER TABLE article MODIFY article_id AUTO_INCREMENT;
ALTER TABLE tag ADD tag_id INT(30) NOT NULL;
ALTER TABLE tag ADD PRIMARY KEY(tag_id);
ALTER TABLE tag MODIFY tag_id AUTO_INCREMENT;
ALTER TABLE tag ADD FOREIGN KEY (tag_id) REFERENCES (article_id);
我想让一篇文章有一对一的分类,然后让文章有一对多的分类。我不能一对一,甚至不能尝试一对多。你能给我一些关于如何实现这一目标以及关系如何运作的见解吗
这是来自数据库内部的信息-
mysql> select * from Tag;
+-------------+----------+--------+
| description | priority | tag_id |
+-------------+----------+--------+
| wtf | 1 | 1 |
| is this | 2 | 2 |
+-------------+----------+--------+
mysql> select * from Article;
+-------+--------------+------------+
| price | published_on | article_id |
+-------+--------------+------------+
| 10 | 2001-01-01 | 7 |
| 20 | 1992-05-08 | 8 |
+-------+--------------+------------+
mysql> describe Article;
+--------------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+---------------+------+-----+---------+----------------+
| price | decimal(30,0) | YES | | NULL | |
| published_on | date | YES | | NULL | |
| article_id | int(30) | NO | PRI | NULL | auto_increment |
+--------------+---------------+------+-----+---------+----------------+
mysql> describe Tag;
+-------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| description | varchar(30) | NO | | NULL | |
| priority | int(30) | NO | | NULL | |
| tag_id | int(30) | NO | PRI | NULL | |
+-------------+-------------+------+-----+---------+-------+ mysql> select * from Tag;
+-------------+----------+--------+
| description | priority | tag_id |
+-------------+----------+--------+
| wtf | 1 | 1 |
| is this | 2 | 2 |
+-------------+----------+--------+
mysql> select * from Article;
+-------+--------------+------------+
| price | published_on | article_id |
+-------+--------------+------------+
| 10 | 2001-01-01 | 7 |
| 20 | 1992-05-08 | 8 |
+-------+--------------+------------+
mysql> describe Article;
+--------------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+---------------+------+-----+---------+----------------+
| price | decimal(30,0) | YES | | NULL | |
| published_on | date | YES | | NULL | |
| article_id | int(30) | NO | PRI | NULL | auto_increment |
+--------------+---------------+------+-----+---------+----------------+
mysql> describe Tag;
+-------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| description | varchar(30) | NO | | NULL | |
| priority | int(30) | NO | | NULL | |
| tag_id | int(30) | NO | PRI | NULL | |
+-------------+-------------+------+-----+---------+-------+
这是我在创建外键时遇到的错误:
mysql> ALTER TABLE Tag ADD FOREIGN KEY(tag_id) REFERENCES Article(article_id);
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`exam_example`.`#sql-2836_1`,
CONSTRAINT `#sql-2836_1_ibfk_1` FOREIGN KEY (`tag_id`) REFERENCES `Article` (`article_id`))
这是一对一的关系
我在这里说,标记的主键与文章中的主键相同。您介意再解释一下问题的具体参数是什么吗?我想我可能可以帮助您,但我仍然不是100%清楚问题是什么。您的SQL创建了两个表
category
和tag
,但是您的INSERT
和ALTER
语句引用的是表文章。另外,为什么不将ALTER
语句滚动到CREATE
语句中呢?我想在article和tag之间创建一对一的关系。“在某个地方我失败了,我不知道在哪里或者为什么失败。”迪诺索费尔朋。我在练习我的alter语句。我想我应该能够在没有钥匙的情况下一对一地完成任务。你认为我把它们放在哪里会有不同吗?你能帮我吗?
CREATE TABLE article (
price INT(30) NOT NULL,
published_on DATE NOT NULL,
article_id INT(30) NOT NULL,
CONSTRAINT pk_article_id PRIMARY KEY(article_id)
);
CREATE TABLE tag(
descption VARCHAR(30) NOT NULL,
priority INT(30) NOT NULL,
tag_id INT(30) NOT NULL,
CONSTRAINT pk_tag_article PRIMARY KEY(tag_id),
CONSTRAINT fk_tag_article FOREIGN KEY(tag_id) REFERENCES article(article_id)
);
INSERT INTO article VALUES (10.0, "2001-01-01", 0);
INSERT INTO article VALUES (20.0, "1992-05-08", 1);
INSERT INTO tag VALUES ("wtf", 1, 1);
INSERT INTO tag VALUES ("is this", 2, 2);