Iterating through rows where rows could be "missing" - sql

Question

I have a table with multiple rows with a column for ordering these rows. And then I have an expired column and a data column:
|ordering| expired | data |
------------------------------
| 1 |2020-12-31|whatever|
| 2 |2020-12-31|whatever|
| 3 |2020-12-31|whatever|
| 4 |2010-01-01|whatever|
| 5 |2020-12-31|whatever|
I also have a table with the line number for which I last got:
|number|
|------|
| 2 |
I get that number and add 1 to get the next line I need. Then I check if that number is higher than the rowcount and got back to 1 if it is. I store the new line back into number so I can use that the next time I need a row.
This is working perfectly except I filter the results by expired. In the above example row 4 will not be selected. So when I get the row with ordering=4 then the result will be empty. Of course it is easy to fix - if I get an empty results I can just try the next value. This takes extra time and lots of extra time if there are lots of expired rows.
I also need to take care that I don't loose a row if a row I previously got happens to get expired between two calls.
What is the most effective way to iterate through rows when they could be constantly changing?

Answer 1

Running the query twice is possibly the best approach. But, you can also order all the results, starting with the first value after the number and wrapping around:
order by (case when t1.ordering > t2.number then 1 else 2 end),
t1.ordering
If you have 10 rows, then this is fine. If you have 10,000 then you incur the overhead of sorting all the data, and two queries are probably faster.

Answer 2

You could perform a query using Min(ordering):
SELECT #nextOrderingNum = Coalesce(Min(t1.ordering), 0)
FROM table1 t1
WHERE t1.expired > GETDATE()
AND t1.ordering > #prevOrderingNum;
If #nextOrderingNum is 0 set #prevOrderingNum = #nextOrderingNum and run again.
Edit, even better instead of running twice just add a sub-query to the Coalesce:
SELECT #nextOrderingNum = Coalesce(Min(t1.ordering),
(SELECT Min(t2.ordering) FROM table1 t2
WHERE t2.expired > GETDATE()))
FROM table1 t1
WHERE t1.expired > GETDATE()
AND t1.ordering > #prevOrderingNum;