Data not getting bind with cursor

Question

Hi,
Database: Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - 64bit
OS: Windows Server 2003
Consider following procedure:
Proc P1() as
cursor c(in_par varchar2) is select distinct col1, col2 from Table1 where col3 = in_par;
begin
for rec_c in c('X') loop
end loop;
exception
end;
Problem: In most of the execution, the value 'X' passed in cursor c get bind with col3 in where clause and get the desired result. However, in some cases, the value 'X' does not get bind with col3 in where clause. I don't know the steps to re-produce the issue, but it occurs once in a while.
On querying v$sql_bind_capture, i get 'NULL' in value_string whenever this problem occurs. Otherwise, I get 'X' in v$sql_bind_capture. No exception is thrown anytime.
What may cause miss of binding constant literal 'X' to cursor?

Answer 1

Have not seen this error before - PL/SQL not binding SQL statements containing PL/SQL variables, correctly. What at times happen is no bind at all due to name collision. Using the same name for a PL/SQL variable as a SQL column in the SQL statement and scope being such that with name resolution, the SQL column gets preference. This of course does not seem to be the case here.
What could be happening is that a null variable is being passed as the bind value.
You can also have a look at the Metalink/support.oracle.com for any notes or bugs on this behaviour. Knee-jerk reaction from my side that this is too a common issue to be an actual PL/SQL bug... (would have reared its head a long time ago)
In cases like this I like to make sanity checks - reduce the problem to its bare basics with a test case and see if that works. Then gradually increase its complexity and see when it brakes, if at all.