Question

I need help to transform data on a table, reducing a series of columns to one single column. An example follows below:

Frequency_1 integer,
Frequency_2 integer,
Frequency_3 integer,
Frequency_4 integer,

These columns currently hold 1 or 0. Only one column will hold 1.

The new column should be defined as

Frequency integer

And this new column should hold a value between 1 and 4, depending on which of the old columns had its value = 1.

Could you suggest an SQL command to accomplish this?

Answer 1

You could come up with something more complicated if you want, but why not just do this?

SELECT Frequency_1 +
       (Frequency_2 * 2) +
       (Frequency_3 * 3) +
       (Frequency_4 * 4) AS Frequency

To actually make the change, you can create the column first, update the value in the new column, then delete the old columns.