SQL Server Management Studio declaring variable [duplicate]

Question

I was doing the following in SQL Server Management Studio

declare @datestring varchar;

BEGIN
   set @datestring ='18/04/2015'
   select @datestring
END

Enough surprisingly for me, the result is 1.

Can someone please explain this?

Answer 1

Try to declare by giving the length to varchar

declare @datestring varchar(10);

If you will not provide any length to varchar then it would default to 1.

From the MSDN:

When n is not specified in a data definition or variable declaration statement, the default length is 1. When n is not specified when using the CAST and CONVERT functions, the default length is 30.

Answer 2

When using the text type variables you should explicitly set the length of the variable:

declare @datestring varchar(10);
BEGIN
    set @datestring ='18/04/2015'
    select @datestring
END

If you do not specify the length it is identical to varchar(1) as described in Remarks section of this MSDN article:

When n is not specified in a data definition or variable declaration statement, the default length is 1. When n is not specified when using the CAST and CONVERT functions, the default length is 30.