What is mean name after variable name in t-sql

I have the next query:

DECLARE @startdate DATETIME
SET @startdate = ''1/1/1990''
;WITH cte
AS (
    SELECT @startdate DateVal
    UNION ALL
    SELECT DateVal + 1
    FROM cte
    WHERE DateVal + 1 <= @enddate
    )

Сan you please explain what it means instruction:

@startdate DateVal

Is a variable called startdate assigned a different name? But why?

Answer

First, I would write this as:

@startdate as DateVal

The two are equivalent, but this is clearer in intent (and less likely to cause problems).

In any case, @startdate is not a valid column name in a table — or CTE. So, you want to give it a valid name. That is what this is doing.

If you don’t give it a name, you will get an error, as illustrated here.

You should also use standard date formats, so I would suggest:

SET @startdate = '1990-01-01';  -- ISO standard format but could be affected by internationalization formats

or:

SET @startdate = '19900101';    -- SQL Server standard format.  Unambiguous.