Declaring a Variable

Introduction

To declare a variable, you use the DECLARE operator in the following formula:

DECLARE @VariableName DataType;

Here is an example:

DECLARE @Category int;

You can also declare more than one variable. To do that, separate them with a comma. The formula would be:

DECLARE @Variable1 DataType1, @Variable2 DataType2, @Variable_n DataType_n;

Unlike many other languages like C/C++, C#, Java, or Pascal, if you declare many variables that use the same data type, the name of each variable must be followed by its own data type.

After declaring a variable, to initialize it, type the SELECT or the SET keyword followed by the name of the variable, followed by the assignment operator "=", followed by an appropriate value. The formula used is:

SELECT @VariableName = DesiredValue

or

SET @VariableName = DesiredValue

Here is an example

DECLARE @Category int
SET @Category = 1450
PRINT @Category
GO

This would produce:

(1 rows affected)
1> DECLARE @Category INT;
2> SET @Category = 1450;
3> PRINT @Category;
4> GO
1450

(1 rows affected)

Here is another example:

1> DECLARE @StudentAge tinyint;
2> SET @StudentAge = 14;
3> SELECT @StudentAge AS [Student's Age];
4> GO
Student's Age
-------------
           14

(1 rows affected)

Here is another example:

1> DECLARE @NumberOfPages SMALLINT;
2> SET @NumberOfPages = 16;
3> SELECT @NumberOfPages AS [Number of Pages];
4> GO
Number of Pages
---------------
             16

(1 rows affected)

Here is another example:

1> DECLARE @CountryPopulation BigInt;
2> SET @CountryPopulation = 16500000;
3> SELECT @CountryPopulation AS 'Country Population';
4> GO
Country Population
--------------------
            16500000

(1 rows affected)

Here is another example:

1> DECLARE @Distance DECIMAL;
2> SET @Distance = 648.16;
3> PRINT @Distance;
4> GO
648

Here is another example:

1> DECLARE @Radius FLOAT;
2> SET @Radius = 48.16;
3> SELECT @Radius AS Radius;
4> GO
Radius
------------------------
      48.159999999999997

(1 rows affected)

Here is another example:

Here is another example:

1> DECLARE @YearlyIncome Money;
2> SET @YearlyIncome = 48500.15;
3> SELECT @YearlyIncome AS [Yearly Income];
4> GO
Yearly Income
---------------------
           48500.1500

(1 rows affected)

Here is another example:

1> DECLARE @IndependenceDay DATETIME;
2> SET @IndependenceDay = '01/01/1960';
3> SELECT @IndependenceDay AS [Independence Day];
4> GO
Independence Day
-----------------------
1960-01-01 00:00:00.000

(1 rows affected)

Here is another example:

1> DECLARE @ArrivalTime datetime;
2> SET @ArrivalTime = '18:22';
3> SELECT @ArrivalTime AS [Arrival Time];
4> GO
Arrival Time
-----------------------
1900-01-01 18:22:00.000

(1 rows affected)