How to select columns from a table which have non null values?

Question

I have a table containing hundreds of columns many of which are null, and I would like have my select statement so that only those columns containing a value are returned. I

Answer 1

I don't think this can be done in a single query. You may need some plsql to first test what columns contain data and put together a statement based on that information. Of course, if the data in your table changes you have to recreate the statement.

declare

   l_table          varchar2(30) := 'YOUR_TABLE';
   l_statement      varchar2(32767);
   l_test_statement varchar2(32767);

   l_contains_value pls_integer;

   -- select column_names from your table
   cursor c is
      select column_name
            ,nullable
        from user_tab_columns
       where table_name = l_table;

begin
   l_statement := 'select ';
   for r in c
   loop
      -- If column is not nullable it will always contain a value
      if r.nullable = 'N'
      then
         -- add column to select list.
         l_statement := l_statement || r.column_name || ',';
      else
         -- check if there is a row that has a value for this column
         begin
            l_test_statement := 'select 1 from dual where exists (select 1 from ' || l_table || ' where ' ||
                                r.column_name || ' is not null)';
            dbms_output.put_line(l_test_statement);
            execute immediate l_test_statement
               into l_contains_value;


            -- Yes, add column to select list
            l_statement := l_statement || r.column_name || ',';
         exception
            when no_data_found then
               null;
         end;

      end if;
   end loop;

   -- create a select statement
   l_statement := substr(l_statement, 1, length(l_statement) - 1) || ' from ' || l_table;

end;