How can I create a loop on an UPDATE statement that works until there is no row left to update?

Question

Assume that I have thousands of rows to update.

And I plan to do the update iteratively; by only updating 1000 rows per iteration.

And I want to iterate until there are no rows left to update.

How can I run the T-SQL script below until there is no row to update?

-- TODO: Create a loop so that it exists when there is no ROW left to be updated; 
-- how can I do it?

UPDATE tableToUpdate
SET IsVegetable = 1
WHERE Id IN
               (SELECT TOP 1000 Id
                FROM tableToUpdate
                WHERE Date = '2011-07-23 14:00')

-- Loop ends

Answer 1

Try this loop

while 1 = 1
BEGIN
    UPDATE top (1000) tableToUpdate
    SET IsVegetable = 1
    WHERE 
        Date = '2011-07-23 14:00'
    AND IsNull(IsVegetable, 0) = 0

    if @@ROWCOUNT < 1000 BREAK
END

Why ISNULL - because it is not clear - if the field IsVegetable is nullable or not, if not - then ISNULL not needed

When there no rows will left with IsVegetable <> 1 - the loop will quit because the @@ROWCOUNT will be = 0 or < 1000 (for the last iteration)