decrement all columns entry when row is deleted
If the objective is to be able to sort the rows according to row_number then don't bother updating values on a delete.  The rows will come out in the same order after a row is deleted as they would before.  It is not worth the effort to close up the gaps.  In the worst case, if you delete the lowest-numbered row, you will have to update every remaining row in the table, in a transaction, with locking and all the concurrency problems that involves.  Don't do it.

If you absolutely must have some visual indication to users then let the application UI produce one, or use a function like ROW_NUMBER() at run time (SQL Server; other RDBMSs have similar).