TSQL set the column value of a table variable

Question

I am trying to set individual columns of a table variable iteratively as follows:

declare @reg_data table
(
    I int NOT NULL PRIMARY KEY IDENTITY,
    Y float
)

declare @counter int, @numRows int
SET @counter = 0
SET @numRows = (select MAX(val) + 10 from tableY)

WHILE @counter < numRows
BEGIN
    SET @reg_data.Y = dbo.func1(@counter)       --HOW DO I DO THIS!!!  
    @counter = @counter + 1
END

The above does not work because you cannot access table variables like an array. How can I obtain the following functionality?

Answer 1

You can't set values in records that doesn't exists, so you need an insert:

WHILE @counter < numRows
BEGIN
    INSERT INTO @reg_data (Y) values (dbo.func1(@counter))
    @counter = @counter + 1
END

Answer 2

Just for the completeness a one-statement example with a CTE and no looping:

DECLARE @reg_data TABLE (
    I INT NOT NULL PRIMARY KEY IDENTITY,
    Y FLOAT
);

WITH cteNum AS (
    SELECT MAX(val) + 10 AS val
    FROM @tableY
    HAVING MAX(val) >= 0
    UNION ALL
    SELECT val-1
    FROM cteNum
    WHERE val > 0
)
INSERT @reg_data(Y)
    SELECT dbo.func1(val)
    FROM cteNum
    OPTION (MAXRECURSION 0);

Answer 3

Why use a cursor for this at all??

Why don't you just write some UPDATE statements:

WHILE @counter < numRows
BEGIN
    UPDATE @reg_data
    SET Y = dbo.func1(@counter)  
    WHERE I = @counter

    SET @counter = @counter + 1
END

You need to somehow be able to read out the identifying values (the I) from the table variable, so you can use that in your UPDATE statement to apply the update to exactly one row (that's identified by that value of I)