When working with SQL Server, it’s important to understand how to use variables and constants in your scripts. In this article, we will explore the basics of working with variables and constants in SQL Server.

Variables in SQL Server

In SQL Server, variables are used to store and manipulate data. They can be declared using the following syntax:

DECLARE @VariableName DataType = Value;

For example, to declare a variable called @Name of type VARCHAR and assign it a value of 'John', you would use the following code:

DECLARE @Name VARCHAR(50) = 'John';

You can then use the variable in your SQL statements, such as:

SELECT * FROM Customers WHERE FirstName = @Name;

Constants in SQL Server

Constants in SQL Server are similar to variables, but their values cannot be changed once they are assigned. They are typically used to store values that are used repeatedly throughout your script.

To declare a constant in SQL Server, you can use the CONST keyword:

CONST @ConstantName DataType = Value;

For example, to declare a constant called @TaxRate of type DECIMAL and assign it a value of 0.08, you would use the following code:

CONST @TaxRate DECIMAL(4,2) = 0.08;

You can then use the constant in your SQL statements, such as:

SELECT ProductName, Price, Price * @TaxRate AS TaxAmount FROM Products;

Using Variables and Constants in SQL Server

Variables and constants can be used in various ways in SQL Server. They can be used in SELECT statements, WHERE clauses, and even in calculations.

For example, you can use a variable to store a value and then use it in a calculation:

DECLARE @Discount DECIMAL(4,2) = 0.10;
SELECT ProductName, Price, Price - (Price * @Discount) AS DiscountedPrice FROM Products;

In this example, we declare a variable called @Discount and assign it a value of 0.10. We then use this variable in the calculation to determine the discounted price of each product.

Similarly, you can use a constant to store a value that is used repeatedly in your script:

CONST @TaxRate DECIMAL(4,2) = 0.08;
SELECT ProductName, Price, Price * @TaxRate AS TaxAmount FROM Products;

In this example, we declare a constant called @TaxRate and assign it a value of 0.08. We then use this constant in the calculation to determine the tax amount for each product.

Conclusion

In this article, we have explored the basics of working with variables and constants in SQL Server. Variables are used to store and manipulate data, while constants are used to store values that do not change. By understanding how to use variables and constants effectively, you can enhance the flexibility and efficiency of your SQL Server scripts.