Select not null columns from a table

When you're talking variable numbers of columns, you are in the territory of dynamic sql, and you are going to have to write some PL/SQL. So you need to change your select based on what is or is not in the columns. I'd start with a select like

DECLARE
  num1_count INTEGER;
  num2_count INTEGER;
  num3_count INTEGER;
  col1_count INTEGER;
  col2_count INTEGER;
  col3_count INTEGER;
  select_cmd VARCHAR2(1000);
BEGIN
SELECT sum(CASE WHEN num1 IS NULL THEN 0 ELSE 1 END) as num1_count,
       sum(CASE WHEN num2 IS NULL THEN 0 ELSE 1 END) as num2_count,
       sum(CASE WHEN num3 IS NULL THEN 0 ELSE 1 END) as num3_count,
       sum(CASE WHEN col1 IS NULL THEN 0 ELSE 1 END) as col1_count,
       sum(CASE WHEN col2 IS NULL THEN 0 ELSE 1 END) as col2_count,
       sum(CASE WHEN col3 IS NULL THEN 0 ELSE 1 END) as col3_count
  INTO num1_countl,num2_count,num3_count,col1_count,col2_count,col3_count
  FROM MY_TABLE; /* add any WHERE clause you will want on the final SELECT */
select_cmd := 'SELECT ';
IF num1_count > 0 THEN select_cmd := select_cmd || 'num1,'; END IF;
IF num2_count > 0 THEN select_cmd := select_cmd || 'num2,'; END IF;
/* continue like this until you added to the SELECT all the columns that have some NOT NULLS */
/* delete that last comma and add your WHERE and ORDER BY clauses */

The next thing you'll need is a OPEN FOR to get a cursor for the SELECT that you build. But that can wait.

What is the desired output if there are no non-NULL values in ANY column of the table? For example, if the table has no rows at the time of execution?