SQL query to remove multiple columns (normalize)

Question

one is often opposed with a filled-in denormalized table, which is although having a primary key, such as:

| RowID  | Column1 | Column2 | Column3 | Column4 | ...
| 'Row1' | 'a1'    | 'a2'    | 'a3'    | 'a4'    |
| 'Row2' | 'b1'    | 'b2'    | 'b3'    | 'b4'    |
| 'Row3' | 'c1'    | 'c2'    | 'c3'    | 'c4'    |
...

Question is: how to efficiently convert it into the 3nf storing the data? (ideally, let's assume that the number of columns and their names are not known)

| RowID | ColumnID | Value |
| 1     | 1        | 'a1'  |
| 1     | 2        | 'a2'  |
...

or, ideally,

| RowID  | ColumnID  | Value |
| 'Row1' | 'Column1' | 'a1'  |
| 'Row1' | 'Column2' | 'a2'  |
...

One solution I'm aware of is selecting columns one under another with a couple of UNIONs, but the script is going to look terrible in case of many columns.

Any help is much appreciated!

Best regards, Constantine.

Answer 1

actually the "Unpivot" operator was what I needed.

Unpivot with column name

Best, Constantine