AND OR precedence in JOIN ON condition

Question

Hi Guys,
I have a small operator precedence problem.
the last part of my LEFT OUTER JOIN clause looks like this:
ON bsch.key# = aknl.key# AND aknl.month =  bsch.month
The above works fine, but there are some cases that need an addition
ON bsch.key# = aknl.key# AND aknl.month =  bsch.month OR aknl.month =  add_months(bsch.month,-1)
The problem is that when I add the extra OR the records that I get without the extra OR dont appear
anymore. I need to introduce some precedence here. When it works without the OR i.e. the normal AND clause
and the = operator then use that first and foremost. Only in case it does not, use the OR clause condition.
Can someone help me with that?
Regards,
metalray
Edited by: metalray on 23.05.2012 02:03

Answer 1

It looks like you want
ON ((bsch.key# = aknl.key# AND aknl.month = bsch.month) OR (aknl.month = add_months(bsch.month,-1)))
and if you don't want the default precedence, just use ()
Sybrand Bakker
Senior Oracle DBA