Leetcode 2253. Dynamic Unpivoting of a Table

Convert a wide table into a long/normalized form by turning a variable set of value-columns into rows (i.e., unpivoting), producing identifier + column-name/ordinal + value tuples. The challenge is that the column set isn’t fixed at query time, so you must dynamically discover/generate the unpivot logic (metadata-driven or dynamic SQL) while preserving semantics such as order and NULL handling.