Report spontaneously stops working

Question

I mentioned in yesterday's post that I cleared an error by re-implementing the page from scratch with the same SQL. The error has recurred, so I'm thinking now that I must be overrunning an internal buffer somewhere. Page 1 is my query-by-example form. Page 2 (duplicated on page 10) is the report of patients found by filling in the query by example form.
The symptoms are that the number of rows returned (on page 2 yesterday and page 10 today) is -175. Depending on the pagination scheme used this shows up differently, but obviously a negative number of rows means that nothing good can subsequently happen. The headers show up but no rows are displayed.
I have tried for several hours to figure out the reproduction conditions but with no real luck. The most recent time it happened when I used the tab to navigate back to the report page, but I checked the session variables and all Page 1 variables referenced in the report are still correctly set. Besides, page 2 ran the identical query successfully.
The condition seems to spontaneously clear itself after a while -- the original page that was broken yesterday (p2) is now working while the re-implementation (p10) is currently broken. Also when you log in as a different workspace user, the both pages work correctly.
Is anyone able to play "spot the bug" on the following. This is the report SQL used on pages 2 and 10:
declare
    conj VARCHAR2(5) := ' AND ';
    qSelect LONG;
    codeFound char(1);
    qFrom LONG;
    qWhere LONG;
    query LONG;
    codeClause LONG;
    codeConj varchar2(10);
  BEGIN
    qSelect := 'SELECT pat.patient_id id_v, pat.patient_id id2, mrn mrn, first_name "first name", last_name "last name", ergn "ERG #", birthdate, creation_date ';
    qFrom := 'FROM patient pat';
    qWhere:= ' WHERE visible =''Y''';
    IF :P1_PATIENT_TYPE != '-' THEN
      qWhere:= qWhere || ' and dx = '''||:P1_PATIENT_TYPE||'''';
    END IF;
    IF :P1_FIRST_NAME is not null THEN
      query := query||conj||'upper(FIRST_NAME) like upper('''||:P1_FIRST_NAME||'%'')';
    END IF;
    IF :P1_LAST_NAME is not null THEN
      query := query||conj|| 'upper(LAST_NAME) like upper('''||:P1_LAST_NAME||'%'')';
    END IF;
    IF :P1_MRN is not null THEN
      query := query||conj|| 'upper(MRN) = upper('''||:P1_MRN||''')';
    END IF;
    IF :P1_ERGN is not null THEN
      query := query||conj|| 'upper(ERGN) =upper('''||:P1_ERGN||''')';
    END IF;
    IF :P1_AGE_START IS NOT NULL THEN
      query := query||conj|| 'trunc( months_between( sysdate, birthdate ) /12 ) >= '||:P1_AGE_START;
    END IF;
    IF :P1_AGE_END IS NOT NULL THEN
      query := query||conj|| 'trunc( months_between( sysdate, birthdate ) /12 ) <= '||:P1_AGE_END;
    END IF;
    IF :P1_AGE_DX_START IS NOT NULL THEN
      query := query||conj|| 'trunc( months_between( creation_date, birthdate ) /12 ) >= '||:P1_AGE_DX_START;
    END IF;
    IF :P1_AGE_DX_END IS NOT NULL THEN
      query := query||conj|| 'trunc( months_between( creation_date, birthdate ) /12 ) <= '||:P1_AGE_DX_END;
    END IF;
    IF :P1_DX_START IS NOT NULL THEN
     query := query||conj||'creation_date >= to_date('''||:P1_DX_START||''',''MM/DD/YYYY'')';
    END IF;
    IF :P1_DX_END IS NOT NULL THEN
     query := query||conj||'creation_date <= to_date('''||:P1_DX_END||''',''MM/DD/YYYY'')';
    END IF;
    IF :P1_4D_CODE1 IS NOT NULL THEN
      codeFound := 'T';
      qFrom := qFrom || ', DX_4D_CODE dx1';
      qWhere := qWhere || conj ||' dx1.patient_Id = pat.patient_Id';
      codeClause := codeClause || codeConj ||' dx1.code= '||:P1_4D_CODE1;
      codeConj := ' '||:P1_4D_AND_OR;
    END IF;
    IF :P1_4D_CODE2 IS NOT NULL THEN
      codeFound := 'T';
      qFrom := qFrom || ', DX_4D_CODE dx2';
      qWhere := qWhere || conj ||' dx2.patient_Id = pat.patient_Id';
      codeClause := codeClause || codeConj ||' dx2.code= '||:P1_4D_CODE2;
      codeConj := ' '||:P1_4D_AND_OR;
    END IF;
    IF :P1_4D_CODE3 IS NOT NULL THEN
      codeFound := 'T';
      qFrom := qFrom || ', DX_4D_CODE dx3';
      qWhere := qWhere || conj ||' dx3.patient_Id = pat.patient_Id';
      codeClause := codeClause || codeConj ||' dx3.code= '||:P1_4D_CODE3;
      codeConj := ' '||:P1_4D_AND_OR;
    END IF;
    IF :P1_4D_CODE4 IS NOT NULL THEN
      codeFound := 'T';
      qFrom := qFrom || ', DX_4D_CODE dx4';
      qWhere := qWhere || conj ||' dx4.patient_Id = pat.patient_Id';
      codeClause := codeClause || codeConj ||' dx4.code= '||:P1_4D_CODE4;
    END IF;
    IF codeFound = 'T' THEN
      query := query||' and ('||codeClause||')';
    END IF;
    return qSelect||qFrom ||qWhere||' '||query;
end;The SQL that is generated is quite vanilla, so I'm thinking it's the process of generating the query that's the issue. Any idea what might be happening here? It's just a matter of time before the users trigger this.
Thanks in advance,
Susan

Answer 1

Susan,
I don't have a clue what would result in a negative row count. Maybe Marc will weigh in on this. I will offer three general suggestions that might be better than nothing:
1. Replace all your LONGs with varchar2(32767). Just in case.
2. Add reset pagination processes for these reports wherever you can. Not sure exactly how to tell you to do that, but there are lots of examples. Perhaps you already do that.
3. Fix your SQL so that it uses bind variables. The way I read your code, you'll end up with distinct SQL statements that will have to be parsed for each invocation of the report where some data (like P1_FIRST_NAME) has changed. This is a fast way to trash the shared pool and slow down your database. The returned value from your function should have as many bind variables in it as possible.
Scott