Creating a foreign key relationship in a SQL Server CE (Compact Edition) Database
SQL Server CE (Compact Edition) is a lightweight and portable version of SQL Server, ideal for use in mobile and embedded applications. Despite its compact size, it still offers powerful features, including the ability to create foreign key relationships between tables.
Foreign key relationships are used to establish a link between two tables in a database. This link is based on a common field or set of fields between the two tables. It ensures referential integrity, meaning that any changes made to the primary key in one table will be reflected in the corresponding foreign key in the other table.
In this article, we will discuss how to create a foreign key relationship in a SQL Server CE database.
Step 1: Create the Primary and Foreign Key Tables
The first step is to create the tables that will be involved in the foreign key relationship. For this example, we will use two tables – “Orders” and “Customers”. The “Orders” table will be the primary key table and the “Customers” table will be the foreign key table.
To create these tables, we will use the following SQL statements:
CREATE TABLE Orders (
OrderID INT PRIMARY KEY,
OrderDate DATETIME,
CustomerID INT
)
CREATE TABLE Customers (
CustomerID INT PRIMARY KEY,
Name VARCHAR(50),
Email VARCHAR(50)
)
Step 2: Add Data to the Tables
Next, we will add some sample data to both tables so that we can establish a relationship between them.
INSERT INTO Orders VALUES (1, '2020-01-01', 1)
INSERT INTO Orders VALUES (2, '2020-02-01', 2)
INSERT INTO Orders VALUES (3, '2020-03-01', 3)
INSERT INTO Customers VALUES (1, 'John Smith', 'john@gmail.com')
INSERT INTO Customers VALUES (2, 'Jane Doe', 'jane@gmail.com')
INSERT INTO Customers VALUES (3, 'Bob Johnson', 'bob@gmail.com')
Step 3: Create the Foreign Key
Now, we will create the foreign key relationship between the two tables. To do this, we will use the ALTER TABLE statement.
ALTER TABLE Orders
ADD CONSTRAINT FK_Orders_Customers
FOREIGN KEY (CustomerID)
REFERENCES Customers(CustomerID)
This statement creates a foreign key constraint named “FK_Orders_Customers” on the “Orders” table. It specifies that the “CustomerID” column in the “Orders” table references the “CustomerID” column in the “Customers” table.
Step 4: Test the Foreign Key
To test the foreign key, we will try to insert a record into the “Orders” table that references a non-existent customer in the “Customers” table.
INSERT INTO Orders VALUES (4, '2020-04-01', 4)
We will get an error message stating that the foreign key constraint has failed. This is because the “CustomerID” 4 does not exist in the “Customers” table. This ensures that our foreign key relationship is working as intended.
Step 5: Update and Delete Records
One of the main benefits of using foreign key relationships is that it allows us to easily update and delete records in our database without causing data inconsistencies.
For example, if we were to update the “CustomerID” of a record in the “Customers” table, the corresponding record in the “Orders” table will also be updated automatically.
Similarly, if we were to delete a record from the “Customers” table, any records in the “Orders” table that reference that customer will also be deleted automatically.
Conclusion
In this article, we have discussed the steps to create a foreign key relationship in a SQL Server CE database. By establishing this relationship, we can ensure data integrity and make it easier to manage our database. SQL Server CE may be a compact version of SQL Server, but it still offers powerful features that allow us to build robust and efficient databases.
