Select non-zero columns

Question

if we have data in the following format:
c1 c2 c3 c4
0 234 0 12
0 111 0 11
0 280 0 38
0 387 0 49
the above no.of columns can be variable
how can we select only non-zero columns - c2 and c4

Answer 1

Hi,
This requires dynamic SQL.
To find if table_x.c1 contains anything except 0 (incluiding NULL), you could say:
SELECT  'TABLE_X', 'COL1'  FROM  dual  WHERE EXISTS (SELECT NULL FROM table_x WHERE NVL (c1, 1) != 0);What you have to do, using dynamic SQL, is write a SELECT statement like that for every column you want to test.
So you'll need a query like
SELECT  'SELECT '''
        || table_name
        || ''', '''
        || column_name
        || ''' FROM dual WHERE EXISTS (SELECT NULL FROM '
        || table_name
        || ' WHERE NVL ('
        || column_name
        || ', 1) != 0);'  -- Omit ';' in PL/SQL
FROM    all_tab_cols
WHERE   ...  -- whatever you needIn SQL*Plus, you can write all of these statements to a SPOOL file, and then execute it by saying @spool_file.
In PL/SQL, you would use EXECUTE IMMEDIATE to run each statement.