title: Issue with union query - select list not compatible
body: <p>Been working on this query for some time now... Keep getting the error "Corrosponding select-list expressions are not compatible. I am selecting the same # of columns in each select statement.</p>
  
  <pre><code>create volatile table dt as (
  SELECT 
  
              gcv.I_SYS_IDV,
               gcv.i_pln,
               gcv.c_typ_cov,
               gcv.d_eff,
               gcv.d_eff_pln,
               gcv.c_sta,
              gcv.d_sta,
              gcv.c_mde_bft_fst,
              gcv.a_bft_fst,
              gcv.c_mde_bft_sec,
               gcv.a_bft_sec,
              gcv.c_mde_bft_trd,
               gcv.a_bft_trd,
               gcv.p_cre_hom,
               gcv.c_cl_rsk,
               gpv.c_val,
               gpv.i_val,
               gcv.c_pol,
               gpv.i_prv
  
  
  
              FROM Pearl_P.tltc906_gcv gcv,
               pearl_p.tltc912_gpv gpv
  
                WHERE  gcv.i_pln &gt; 0
              AND gcv.i_pln = gpv.i_pln
              and gpv.i_prv = '36'
              and gcv.c_pol between 'lac100001' and 'lac100004'
  
           UNION
  
               SELECT
               gcv.I_SYS_IDV,
               gcv.i_pln,
               gcv.c_typ_cov,
               gcv.d_eff,
               gcv.d_eff_pln,
               gcv.c_sta,
               gcv.d_sta,
               gcv.c_mde_bft_fst,
               gcv.a_bft_fst,
               gcv.c_mde_bft_sec,
               gcv.a_bft_sec,
               gcv.c_mde_bft_trd,
               gcv.a_bft_trd,
               gcv.p_cre_hom,
               gcv.c_cl_rsk,
               gcv.c_pol,
               gpv.i_val,
              gpv.i_pln,
               gpv.i_prv
  
  
          FROM Pearl_P.tltc906_gcv gcv,
          pearl_p.tltc912_gpv gpv
  
  
              where NOT EXISTS(
              SELECT 1
              FROM pearl_p.tltc906_gcv gcv,
               pearl_p.tltc912_gpv gpv
  
              WHERE  gcv.i_pln &gt; 0
              AND gcv.i_pln = gpv.i_pln
              and gpv.i_prv = '36'
              )
          ) with data 
  PRIMARY INDEX (i_sys_idv)
  on commit preserve rows;
  </code></pre>