title: Error ORA-00932 when using a select with union and CLOB fields
body: <p>First of all, this isn't a duplicate of <a href="https://stackoverflow.com/questions/12980038/ora-00932-inconsistent-datatypes-expected-got-clob">this</a> question. If it is, sorry but I couldn't solve my problem by reading it.</p>
  
  <p>I'm getting this error:</p>
  
  <pre><code>ORA-00932: inconsistent datatypes: expected - got CLOB
  </code></pre>
  
  <p>When I try to execute this SELECT statement:</p>
  
  <pre><code>SELECT TXT.t_txt 
    FROM CITADM.tb_avu_txt_grc GR  
   INNER JOIN CITADM.tb_avu_txt TXT   
      ON (GR.e_txt = TXT.e_txt and GR.u_txt = TXT.u_txt)  
   WHERE  TXT.u_lin_ord = 1
  UNION
  SELECT TXT.t_txt 
    FROM CITADM.tb_avu_txt_grc_cvd GRC  
   INNER JOIN CITADM.tb_avu_txt TXT  
      ON (GRC.e_txt = TXT.e_txt and GRC.u_txt = TXT.u_txt)  
   WHERE  TXT.u_lin_ord = 2
  </code></pre>
  
  <p>The selected field(t_txt) is of CLOB datatype. As you can see, it's the same column of the same table. This statement belongs to a bigger one, I've isolated the part where I'm having this problem.</p>
  
  <p>Thank you very much.</p>