FOREIGN KEY in the "Orders" table. The FOREIGN KEY constraint prevents invalid data from being inserted into the foreign key column, because it has to be one of the values contained in the parent table. The following SQL creates a FOREIGN KEY on the "PersonID" column when the "Orders" table is created:

2024年1月25日 · In PostgreSQL, a foreign key is a column or a group of columns in a table that uniquely identifies a row in another table. A foreign key establishes a link between the data in two tables by referencing the primary key or a unique constraint of the referenced table.

2024年12月27日 · In this article, we have mentioned the primary key and foreign key, and the differences between them. Both the keys, whether the primary key or the foreign key, play an important role in the Database management system. Primary Key contains unique values, whereas Foreign Key contains values taking reference from Primary Keys.

2024年10月9日 · In this PostgreSQL foreign key tutorial, we’ll cover how foreign keys work, their importance and how to create them. We will also learn about foreign key constraints and their role in ensuring data consistency. By the end, we will have a solid understanding of what a foreign key is in PostgreSQL and how to implement it effectively.

2025年2月4日 · This article describes how to create foreign key relationships in SQL Server by using SQL Server Management Studio or Transact-SQL. You create a relationship between two tables when you want to associate rows of one table with rows of another.

2017年9月13日 · FK应该在 角色表上； FK设定的重要原则：FK必然是另一个表的PK的映射。 （做FK的不一定是PK字段） FK 的好处：可以使得两张表关联，保证数据的一致性和实现一些级联操作。 ---- 还有好多的不懂之处，后续知道了再补充。 文章浏览阅读1.9w次。 本文用于博主自身记录遇到的问题以及解决办法。 _fk的用法.

Summary: in this tutorial, you will learn about the SQL foreign key and how to create a FOREIGN KEY constraint to enforce the relationship between tables. A foreign key is a column or a group of columns that enforces a link between the data in two tables.

2025年1月15日 · By linking a child table to a parent table, the foreign key establishes referential integrity. This constraint ensures that the values in the foreign key column match the primary key values in the referenced table, thereby maintaining consistent and valid data across the database.

FK names are in the global namespace in SQL Server so you can't have two FKs named FK_PrimaryKeyTable attached to two different foreign key tables. The rules may be different for other database servers.

ALTER TABLE child_table ENABLE CONSTRAINT fk_name; Code language: SQL (Structured Query Language) (sql) In this tutorial, you have learned how to use the Oracle foreign key constraint to enforce the relationship between tables.