In the world of databases, one of the most important aspects is maintaining data integrity. This includes making sure that all records are unique and accurate. One way to ensure this is by using auto-incrementing fields. In this article, we will explore how to implement this feature in MS SQL Server 2005, specifically for fields that are not primary keys.
First, let's understand what an auto-incrementing field is. Simply put, it is a field in a database table that automatically increases its value by a specified amount each time a new record is inserted. This ensures that each record has a unique identifier, making it easier to retrieve and manage data.
To begin, we need to create a table in our database. Let's call it "Customers" and give it four columns - "CustomerID", "Name", "Email", and "Phone". We want the "CustomerID" column to be auto-incrementing, so we will set it as an integer data type and add the keyword "IDENTITY(1,1)" after the data type. This specifies that the field will start at 1 and increment by 1 for each new record.
CREATE TABLE Customers (
CustomerID INT IDENTITY(1,1) PRIMARY KEY,
Name VARCHAR(50),
Email VARCHAR(50),
Phone VARCHAR(20)
);
Next, we need to insert some data into our table. We can do this using the INSERT statement, but we will not include any value for the "CustomerID" column since it will be automatically generated.
INSERT INTO Customers (Name, Email, Phone)
VALUES ('John Smith', 'johnsmith@email.com', '555-123-4567'),
('Jane Doe', 'janedoe@email.com', '555-987-6543'),
('Bob Johnson', 'bjohnson@email.com', '555-678-9012');
If we query the table, we will see that the "CustomerID" column has been automatically incremented for each record, starting at 1 and increasing by 1.
SELECT * FROM Customers;
CustomerID | Name | Email | Phone
-----------|------------|----------------------|-------------
1 | John Smith | johnsmith@email.com | 555-123-4567
2 | Jane Doe | janedoe@email.com | 555-987-6543
3 | Bob Johnson| bjohnson@email.com | 555-678-9012
But what if we want to start the auto-incrementing field at a different value? For example, we may already have some records in our table with manually assigned IDs and want to continue the auto-incrementing from where we left off. In that case, we can use the SET IDENTITY_INSERT statement.
Let's say we have five records in our "Customers" table with IDs 1 through 5. To continue the auto-incrementing from 6, we can use the following statement:
SET IDENTITY_INSERT Customers ON;
INSERT INTO Customers (CustomerID, Name, Email, Phone)
VALUES (6, 'Sam Smith', 'samsmith@email.com', '555-246-8013'),
(7, 'Sara Johnson', 'sjohnson@email.com', '555-135-7911');
SET IDENTITY_INSERT Customers OFF;
Now when we query the table, we will see that the "CustomerID" column has continued incrementing from 6.
SELECT * FROM Customers;
CustomerID | Name | Email | Phone
-----------|--------------|-----------------------|-------------
1 | John Smith | johnsmith@email.com | 555-123-4567
2 | Jane Doe | janedoe@email.com | 555-987-6543
3 | Bob Johnson | bjohnson@email.com | 555-678-9012
6 | Sam Smith | samsmith@email.com | 555-246-8013
7 | Sara Johnson | sjohnson@email.com | 555-135-7911
Lastly, let's explore how to update an auto-incrementing field. In order to do this, we will need to use the SET IDENTITY_INSERT statement again. We can also use the UPDATE statement to change the value of the auto-incrementing field for a specific record.
SET IDENTITY_INSERT Customers ON;
UPDATE Customers
SET CustomerID = 4
WHERE Name = 'John Smith';
SET IDENTITY_INSERT Customers OFF;
Now when we query the table, we will see that the "CustomerID" for John Smith has been updated to 4.
