Re: Do all the legs of an "OR" with null comparisons get executed?

From: Charles Hooper <hooperc2000_at_yahoo.com>
Date: Sat, 29 Mar 2008 10:43:34 -0700 (PDT)
Message-ID: <6c1e95e0-534b-475b-bbc4-d2955ebc619c@d21g2000prf.googlegroups.com>

On Mar 28, 5:43 pm, Arthernan <arther..._at_hotmail.com> wrote:
> If I do an explain plan of the statement below I can see that the
> "and" clauses that have MMDDOB=NULL do not get executed
>
> select * from v_search where
> UPP_FIRST='JOHN' and UPP_LAST='SMITH' and MMDDOB=NULL and AA=1 or
> UPP_FIRST='JOHN' and UPP_LAST='SMITH' and BB=2 or
> UPP_FIRST='JOHN' and UPP_LAST='SMITH' and CC='CA' or
> UPP_FIRST='JOHN' and MMDDOB=NULL and AA=1 and BB=2 or
> UPP_FIRST='JOHN' and MMDDOB=NULL and AA=1 and CC='CA' or
> UPP_FIRST='JOHN' and BB=2 and CC='CA' or
> UPP_LAST='SMITH' and MMDDOB=NULL and AA=1 and BB=2 or
> UPP_LAST='SMITH' and MMDDOB=NULL and AA=1 and CC='CA' or
> UPP_LAST='SMITH' and BB=2 and CC='CA' or
> MMDDOB=NULL and AA=1 and BB=2 and CC='CA'
>
> My problem is how to know if it does the same thing when I parametize
> the query as
>
> select * from v_search where
> UPP_FIRST=:UPP_FIRST and UPP_LAST=:UPP_LAST and MMDDOB=:MMDD and
> AA=:AA or
> UPP_FIRST=:UPP_FIRST and UPP_LAST=:UPP_LAST and BB=:BB or
> UPP_FIRST=:UPP_FIRST and UPP_LAST=:UPP_LAST and CC=:CC or
> UPP_FIRST=:UPP_FIRST and MMDDOB=:MMDD and AA=:AA and BB=:BB or
> UPP_FIRST=:UPP_FIRST and MMDDOB=:MMDD and AA=:AA and CC=:CC or
> UPP_FIRST=:UPP_FIRST and BB=:BB and CC=:CC or
> UPP_LAST=:UPP_LAST and MMDDOB=:MMDD and AA=:AA and BB=:BB or
> UPP_LAST=:UPP_LAST and MMDDOB=:MMDD and AA=:AA and CC=:CC or
> UPP_LAST=:UPP_LAST and BB=:BB and CC=:CC or
> MMDDOB=:MMDD and AA=:AA and BB=:BB and CC=:CC
>
> On Mar 28, 2:15 pm, Frank van Bortel <frank.van.bor..._at_gmail.com>
> wrote:
>
>
>
>
>
> > Arthernan wrote:
> > > That is an alternative. I do think the logic is correct thought. Take
> > > the first comparison for example:
>
> > > UPP_FIRST='JOHN' and UPP_LAST='SMITH' and MMDDOB=NULL and AA=1
>
> > MMDDOB=NULL should be "MMDDOB is NULL"
>
> > And no, Oracle is smart enough to know boolean algebra; if
> > a part of the boolean equation yields true (or false), the
> > rest is no executed - it would not change the outcome.
>
> > Now, you figure out when to OR or AND, and when TRUE or
> > FALSE :)
> > --
>
> > Regards,
> > Frank van Bortel
>
> > Top-posting in UseNet newsgroups is one way to shut me up
>
> But if I did "MMDDOB is NULL" instead of MMDDOB=NULL. I would get
> records back when I don't want them.
>
> The final query will be parametized like this  "MMDDOB=:MMDDOB". So I
> want to know if :MMDDOB happens to be NULL, will oracle be smart
> enougth to realize that whole "and clause" can go away. For example if
> I did MMDDOB=1231, whenever MMDDOB was NULL the row would be filtered
> out. Just look at my original SQL above and you will see what I mean.
>
> Arturo Hernandez- Hide quoted text -
>
> - Show quoted text -

Look closely at the responses that Frank van Bortel provided to you. The WHERE clause is not working the way you expect, and that is why you receive too many rows when using MMDDOB IS NULL.

Placing ( ) as Oracle would evaluate the WHERE clause:

(((((((((((((((((((((((((((((((((((UPP_FIRST='JOHN' and
UPP_LAST='SMITH') and MMDDOB=NULL) and AA=1) or {UPP_FIRST='JOHN') and

UPP_LAST='SMITH') and BB=2)} or UPP_FIRST='JOHN') and UPP_LAST='SMITH') and CC='CA') or UPP_FIRST='JOHN') and MMDDOB=NULL)

and AA=1) and BB=2) or UPP_FIRST='JOHN') and MMDDOB=NULL) and AA=1)
and CC='CA') or {UPP_FIRST='JOHN') and BB=2) and CC='CA')} or
UPP_LAST='SMITH') and MMDDOB=NULL) and AA=1) and BB=2) or
UPP_LAST='SMITH') and MMDDOB=NULL) and AA=1) and CC='CA') or

UPP_LAST='SMITH') and BB=2) and CC='CA') or MMDDOB=NULL) and AA=1) and BB=2) and CC='CA')

Now, let's just replace MMDDOB=NULL with FALSE, as it can never be TRUE (as indicated by several people in this thread):

(((((((((((((((((((((((((((((((((((UPP_FIRST='JOHN' and
UPP_LAST='SMITH') and FALSE) and AA=1) or {UPP_FIRST='JOHN') and

UPP_LAST='SMITH') and BB=2)} or UPP_FIRST='JOHN') and UPP_LAST='SMITH') and CC='CA') or UPP_FIRST='JOHN') and FALSE) and AA=1) and BB=2) or UPP_FIRST='JOHN') and FALSE) and AA=1) and CC='CA') or {UPP_FIRST='JOHN') and BB=2) and CC='CA')} or UPP_LAST='SMITH') and FALSE) and AA=1) and BB=2) or UPP_LAST='SMITH') and FALSE) and AA=1) and CC='CA') or UPP_LAST='SMITH') and BB=2) and CC='CA') or FALSE) and AA=1) and BB=2) and CC='CA')

Now, let's go through the WHERE clause and set all other conditions to TRUE, just to see what happens if those conditions were TRUE:

(((((((((((((((((((((((((((((((((((TRUE and TRUE) and FALSE) and TRUE)

or TRUE) and TRUE) and TRUE) or {TRUE) and TRUE) and TRUE)} or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and TRUE) and TRUE) or FALSE) and TRUE) and TRUE) and TRUE)

In the above, look closely for the curly brackets { } (I did not identify all such cases). Now, simplifying the above a little, we start to see the problem - most of the WHERE clause evaluates to FALSE - always

((((((((((((((((((((((((((((((FALSE or TRUE) and TRUE) and TRUE) or
TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and
TRUE) or TRUE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and

TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and TRUE) and TRUE) or FALSE) and TRUE) and TRUE) and TRUE)

Simplifying again

(((((((((((((((((((((((((((TRUE) or TRUE) and FALSE) and TRUE) and
TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and TRUE) and
TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and FALSE) and

TRUE) and TRUE) or TRUE) and TRUE) and TRUE) or FALSE) and TRUE) and TRUE) and TRUE)

There are only a couple of conditions in the above that could possibly evaluate to TRUE.

The reason that the WHERE clause does not work with the MMDDOB IS NULL condition is due to the order of evaluation. You did not specify the evaluation order by using ( ) in the WHERE clause, so Oracle used the default (note that the default evaluation order differs from some programming languages, such as C).

Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc. Received on Sat Mar 29 2008 - 12:43:34 CDT