Fill the gaps in SQL Server

update.sql

/*
There is a table in database. This table contains unduplicated natural numbers. There may be gaps in the sequence of natural numbers in the table. You need to output missing numbers.
Table of natural numbers: declare @values as table ([number] int not null).
Test data: insert into @values([number]) values (1), (2), (3), (5), (9).
Result: declare @missing as table ([left] int not null, [right] int not null).
*/

DECLARE @values AS TABLE ([number] INT NOT NULL);
INSERT INTO @values([number]) VALUES (1), (2), (3), (5), (9);
DECLARE @missing AS TABLE ([left] INT NOT NULL, [right] INT NOT NULL)

INSERT INTO @missing 
SELECT v.number + 1, next.number - 1
FROM
	@values v
LEFT JOIN @values next
	ON next.number = (
		SELECT TOP 1
			tmp.number
		FROM
			@values tmp
		WHERE
			tmp.number > v.number
	)
WHERE
	v.number + 1 <> next.number
ORDER BY
	v.number
	
/*
Alternative style...

DECLARE @values AS TABLE ([number] INT NOT NULL);
INSERT INTO @values([number]) VALUES (1), (2), (3), (5), (9);
DECLARE @missing AS TABLE ([left] INT NOT NULL, [right] INT NOT NULL)

-- Keeps the previous and next numbers
DECLARE @previous AS INTEGER, @next AS INTEGER;

-- Fast forward cursor to find the holes
DECLARE rsValues CURSOR FAST_FORWARD FOR
	SELECT number
	FROM @values
	ORDER BY number;

OPEN rsValues;
-- Saves the first number
FETCH NEXT FROM rsValues INTO @previous;
WHILE @@FETCH_STATUS = 0
BEGIN
	-- Gets the next number
	FETCH NEXT FROM rsValues INTO @next;
	-- If the next number is breaking the sequence, logs the hole to the @missing table
	IF @@FETCH_STATUS = 0 AND @previous + 1 <> @next
		INSERT INTO @missing VALUES (@previous + 1, @next - 1);
	-- Updates the last number
	SET @previous = @next;
END;  
CLOSE rsValues;  
DEALLOCATE rsValues;
*/