Query started getting 1722 error - interesting explanation why

I got a call from a developer the other week complaining that a query in QA
had started giving an ora-1722.  It had worked fine for several months and
the identical query was working fine in production.

 

Select count(1) 

from prod.job_profile jp

where step_id < 9999

and not exists (select 'x' from prod.job_log jl

                where jl.job_id = jp.job_id

                and ( jl.status in ('C', 'EI') )

                and  jl.batch_id in (select to_number(text_value)

                                     from prod.batch_parameter

                                     where name = 'BATCH_ID'));

 

Investigating confirmed this, along with the fact that the query was
comparing a string (jl.batch_id) with a number (to_number(text_value)).  But
why did it suddenly stop working and why did it still work in production?

 

Comparing explain plans between QA and production I saw that they were
different (statistics had changed during QA testing).  The query that failed
was using an index on jl.batch_id.  

 

Apparently Oracle automatically took care of converting the string to a
number *unless* the number was being used to access an index on the varchar2
column.  Interesting behavior.  I can see why it might work that way but
it's certainly not intuitive. 

 

Of course explaining this to the developer took quite a while.  "It worked
before, why shouldn't it work now?  What's wrong with Oracle?"

 

Oracle 9.2.0.6

 

 

Jay Miller

Sr. Oracle DBA

 

.




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