CODEWITHSUNDEEP
sql-serversql-server-2008-r2
MAK
MAK

Reputation: 7260

Difference between @@ and @ in SQL Server 2008 R2

I am using SQL Server 2008 R2.

My question is What is the difference between declaring variables by using @ and @@?

In SQL Server 2008 R2:

Example:

Syntax 1:

Declare @a int = 1

select @a;

Syntax 2:

Declare @@a int = 1

select @@a;

Both does the same job here. Then why should we use double @@?

Upvotes: 1

Views: 6545

Answers (2)

Marx Izalias
Marx Izalias

Reputation: 1

The other user is not correct, they are not EXACTLY the same.

CREATE PROCEDURE [dbo].[JustWriteLetter]
    @@letter1 nvarchar(1) = 'A',
    @letter2 nvarchar(1) = 'B'
AS
BEGIN
   SELECT @@letter1,@letter2
END;

When you run this code and refresh your parameters... you will get this.Insightful message about how the first param has no default, even though it does.

But when you run the procedure with no params...

It acts in an unexpected, expected way.

So when you use @@ with a default parameter, SQL is just... well, going to lie to you about having a default parameter... it's a bug that's also a feature.

Upvotes: 0

Virbhadrasinh
Virbhadrasinh

Reputation: 539

There is no difference. The rules for variables state that they start with an '@' character and follow the rules for identifiers.

Since '@' is a valid identifier character, you can have as many as you like at the start of your variable name. However, if you match a system function which has the same name as your variable, then the query will not compile.

In previous versions of SQL Server @ described a local variable and @@ describe a global variable. Now (SQL 2008) @@ is used for a function name so @@ shouldnt be used as a parameter name.

Books OnLine ref http://msdn.microsoft.com/en-us/library/ms187953.aspx

if any other problem comment me :)

Upvotes: 7

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