Creating an Identity Column Using SQL Server IDENTITY Property
In databases, an identity column is a column that automatically generates a unique value when a new row is added to a table. The SQL Server IDENTITY property can be used to create identity columns.
In this section, we will explain the syntax of the IDENTITY property, give an example of creating a table with an identity column, and discuss the issue of reusing identity values and gaps in the identity column.
Syntax and Explanation of IDENTITY Property
To create an identity column using SQL Server, you need to use the IDENTITY property, which is a column property. The syntax for using the IDENTITY property is as follows:
Column_Name data_type IDENTITY
(start_value,increment_value)
The “Column_Name” is the name of the column you want to create with the IDENTITY property, the “data_type” is the data type of the column, the “start_value” is the value that the identity column should start from, and the “increment_value” is the value that should be added to the identity column for each new row.
For example, if you want to create an identity column named OrderID for a table called Orders, you can use the following SQL query:
CREATE TABLE Orders
(
OrderID int IDENTITY
(1,1),
CustomerID int,
OrderDate date
)
In this case, the OrderID column would automatically generate unique integers starting from 1 for each new row added to the Orders table.
Example of Creating a Table with an Identity Column
To create a table with an identity column, you can use the CREATE TABLE statement with the IDENTITY property. The following SQL query creates a table called Customers with an identity column named CustomerID:
CREATE TABLE Customers
(
CustomerID int IDENTITY
(1,1) PRIMARY KEY,
FirstName varchar
(50),
LastName varchar
(50),
Email varchar
(100)
)
In this example, the primary key of the Customers table is the CustomerID column, which is an identity column that automatically generates a unique integer starting from 1 for each new row.
Reusing of Identity Values and Loss of Identity Value
One of the issues that can arise with identity columns is the reuse of identity values. When a row is deleted from a table that has an identity column, the identity value is not reused automatically.
This can lead to gaps in the identity column, which can be confusing for users. For example, if a row with an OrderID of 3 is deleted from the Orders table, the next row added to the table would have an OrderID of 4, even though there is a gap where the OrderID 3 used to be.
To avoid the reuse of identity values and gaps in the identity column, you can use the following SQL query:
DBCC CHECKIDENT
(‘Orders’, RESEED, 1)
This query resets the identity value to 1 for the Orders table. However, it should be noted that resetting the identity value can lead to data inconsistency if there are other tables that reference the Orders table.
Creating a New Schema Named hr
In SQL Server, a schema is a container that holds database objects like tables, views, and stored procedures. Schemas can be used to organize database objects and assign permissions to users.
In this section, we will give an example of creating a new schema named hr.
Example of Creating a New Schema Named HR
To create a new schema named hr, you can use the CREATE SCHEMA statement. The following SQL query creates a new schema called hr:
CREATE SCHEMA hr
After creating the schema, you can create tables, views, and other database objects within the hr schema by specifying the schema name before the object name. For example, to create a table named Employees within the hr schema, you can use the following SQL query:
CREATE TABLE hr.Employees
(
EmployeeID int,
FirstName varchar
(50),
LastName varchar
(50),
DOB date,
Salary decimal
(10,2)
)
In this example, the Employees table is created within the hr schema, and the schema name is specified before the table name.
Conclusion
In this article, we have discussed two important topics related to SQL Server database management: creating an identity column using the SQL Server IDENTITY property and creating a new schema named hr. By working through the examples provided, you should now have a better understanding of how each of these features works and how they can be used to optimize your SQL Server database.
Remember, SQL Server offers a wealth of powerful tools for database management, and by taking advantage of them, you can ensure that your databases are organized, secure, and efficient.
3) Inserting Rows and Assigning Positions in the Person Table
In SQL Server, you can insert rows into a table using the INSERT INTO statement. In this section, we will cover how to create and insert data into two tables, as well as how to assign a person a position with a new row insertion.
Creating and Inserting Data into Two Tables
Suppose we have two tables: Person and Position. Person is a table that contains information about people, including their names and dates of birth.
Position is a table that contains information about job positions, including the position title and the salary. To create the Person table, we can use the following SQL query:
CREATE TABLE Person
(
ID int IDENTITY
(1,1) PRIMARY KEY,
FirstName varchar
(50),
LastName varchar
(50),
DateOfBirth date
To create the Position table, we can use the following SQL query:
CREATE TABLE Position
(
ID int IDENTITY
(1,1) PRIMARY KEY,
Title varchar
(50),
Salary decimal
(10,2)
Next, we can insert some data into the tables using the INSERT INTO statement.
Suppose we want to insert a new person named John Smith, who was born on January 1, 1980, and a new position for a software engineer with a salary of $80,000. We can use the following SQL queries to accomplish this:
INSERT INTO Person
(FirstName, LastName, DateOfBirth)
VALUES
(‘John’, ‘Smith’, ‘1980-01-01’);
INSERT INTO Position
(Title, Salary)
VALUES
(‘Software Engineer’, 80000.00);
After executing these queries, we should have a new row in each table: one for John Smith in the Person table and one for the software engineer position in the Position table.
Assigning a Person a Position with a New Row Insertion
Suppose we want to assign John Smith to the software engineer position. We can accomplish this by inserting a new row into a third table, called PersonPosition, that associates John Smith with the software engineer position.
First, we need to get the IDs of the John Smith and software engineer position records in their respective tables. We can use the following SQL queries to retrieve the IDs:
SELECT @@IDENTITY
This query returns the identity value of the most recently added row in a table.
After inserting John Smith into the Person table, we can use this query to retrieve his ID. SELECT ID FROM Position WHERE Title = ‘Software Engineer’
This query retrieves the ID of the software engineer position by searching for the record with the title ‘Software Engineer’ in the Position table.
Next, we can use these IDs to insert a new row into the PersonPosition table, which associates John Smith with the software engineer position. We can use the following SQL query:
BEGIN TRANSACTION
INSERT INTO PersonPosition
(PersonID, PositionID)
VALUES
(@person_id, @position_id)
COMMIT TRANSACTION
In this query, we first start a transaction using the
BEGIN TRANSACTION statement. This ensures that the entire operation executes atomically, meaning that either all of the inserts succeed or none of them do.
We then insert a new row into the PersonPosition table, specifying the IDs of John Smith and the software engineer position. Finally, we commit the transaction using the
COMMIT TRANSACTION statement.
After executing this query, we should have a new row in the PersonPosition table that associates John Smith with the software engineer position.
4) Summary
In this article, we have covered two important topics related to SQL Server database management: creating an identity column using the SQL Server IDENTITY property and inserting rows into tables. By working through the examples provided, you should now have a better understanding of how to create tables with identity columns and insert data into them using the INSERT INTO statement.
Additionally, we covered how to assign a person a position with a new row insertion, using transactions to ensure that the operation executes atomically. Remember, SQL Server offers a wealth of powerful tools for database management, and by taking advantage of them, you can ensure that your databases are organized, secure, and efficient.
In this informative article, we have explored two crucial topics in SQL Server database management: creating an identity column using the SQL Server IDENTITY property and inserting rows into tables. We’ve learned how to create tables with identity columns, insert data using the INSERT INTO statement, and how to assign a person a position with a new row insertion using transactions.
By leveraging these powerful SQL Server tools, one can create efficient and organized databases. The key takeaways are that SQL Server offers robust features for database management, and by employing them, one can ensure secure, organized, and efficient databases.