Question

This SQL Server 2005 T-SQL code:

DECLARE @Test1 varchar;
SET @Test1 = 'dog';

DECLARE @Test2 varchar(10);
SET @Test2 = 'cat';

SELECT @Test1 AS Result1, @Test2 AS Result2;

produces:

Result1 = d
Result2 = cat

I would expect either

1. The assignment SET @Test1 =
'dog'; to fail because there isn’t
   enough room in @Test1
2. Or the SELECT to return ‘dog’ in the Result1 column.

What is up with @Test1? Could someone please explain this behavior?

Answer 1

Let me answer with some quotes from the SQL Server documentation.

char and varchar

varchar[(n)]

…

When n is not specified in a data definition or variable declaration statement, the default length is 1.

Converting Character Data

When character expressions are converted to a character data type of a different size, values that are too long for the new data type are truncated.

So, your varchar is declared as a varchar(1), and the implicit conversion in your SET statement (from a string literal of length 3 to a varchar(1)) truncates dog to d.