Variables are used as a means to assign values in code rather than hard coding values. In simple examples, variables may seem excessive, but they are a good concept to understand as your development skills progress.
In this example, we are going to slightly change the first example to use variables in the INSERT command rather than hard coded values.
Let's explain what's going on with this code:
In the first block of code, we are declaring a variable for each column. All of the data types for the variables match the columns.
In the second block of code, we are setting each of the variables to a value. Note that the varchar and datetime columns have their values in single quotes and integer values are not in single quotes.
In the third block of code, this should look similar to the example above except the code in the 'VALUES' section includes the variables and not the actual values.
-- 1 - Declare variables
DECLARE @FirstName varchar(25)
DECLARE @LastName varchar(25)
DECLARE @PhoneNumber varchar(15)
DECLARE @EmailAddress varchar(25)
DECLARE @Priority int
DECLARE @CreateDate datetime
-- 2 - Initialize variables
SET @FirstName = 'Kris'
SET @LastName = 'Fierce'
SET @PhoneNumber = '222-222-2222'
SET @EmailAddress = 'kris@FierceFishing.com'
SET @Priority = 1
SET @CreateDate = '2011-09-15'
-- 3 - Execute INSERT command
INSERT INTO [dbo].[Customer]