1 mysql使用foreign key 设置外键,php中也可以使用命令来这样做语句是create table example3(id int,stu_id int,course_id int,constraint stu_f foreign key(stu_id,corse_id) references example2(stu_id,course_id)); 即可其中 constraint stu_f foreign key(stu_id,corse_id) references example2(stu_...
现在,我们可以向Customers表和Orders表中插入一些数据,以验证外键的效果。 -- 插入顾客数据INSERTINTOCustomers(customer_id,customer_name,customer_email)VALUES(1,'John Doe','john.doe@example.com');-- 插入订单数据INSERTINTOOrders(order_id,order_date,customer_id)VALUES(1,'2022-01-01',1); 1. 2. ...
FOREIGN KEY foreign_key_name(columns) REFERENCES parent_table(columns) ON DELETE action ON UPDATE action; MySQL adding foreign key example# Now, let’s add a new table named vendors and change the products table to include the vendor id field: 1 2 3 4 5 6 7 8 9 USE dbdemo; CREATE...
通过上述代码中的FOREIGN KEY定义,我们已经在创建posts表的时候同时定义了外键约束。当我们插入数据时,MySQL 会检查外键约束是否得到满足。 4. 测试外键约束 我们可以测试外键的工作方式,通过添加数据到users表和posts表。以下是代码示例: -- 插入用户INSERTINTOusers(username,email)VALUES('john_doe','john@example.c...
This following example relates parent and child tables through a single-column foreign key and shows how a foreign key constraint enforces referential integrity. Create the parent and child tables using the following SQL statements: CREATE TABLE parent ( id INT NOT NULL, PRIMARY KEY (id) ) ...
MySQL foreign keys and ON UPDATE and ON DELETE MySQL foreign keyFAQ: How do I define a foreign key in MySQL? Answer: Here's a quick example of how I typically define a foreign key in MySQL. Diving right into an example, here's the definition for a MySQL database table namednodesthat...
TheForeign Keyssubtab is organized in much the same fashion as theIndexessubtab and adding or editing a foreign key is similar to adding or editing an index. The following figure shows an example of theForeign Keystab. Figure 8.16 The Foreign Keys Tab ...
Foreign KeyPosted by: Daniel Ramirez Date: October 05, 2005 01:33PM HI everybody I'm tryng to find a way to know if a field is a foreign key, by example if I run this describe ; in the "Key" colum I got "PRI" for the primary key field, somebody know a way to get th...
Example cases: If the two fields (Field name and the Foreign Field name) are using incompatible field type. If you use "On Delete Set Null" but the field doesn't allow null. To declare foreign keys in MySQL, there are few points which user should bear in mind: ...
If I have a FOREIGN key in a table can the data in that key be accessed. Example I have in a table a column MFG-PART-NUM and I have a FOREIGN KEY added to the table which is the same as MFG-PART-NUMBER (the generated name can be different but they are the same) do I now ...