Re: Just as a learning exercise
- From: Rumpi Gravenstein <rgravens@xxxxxxxxx>
- To: ric.van.dyke@xxxxxxxxxx
- Date: Wed, 4 May 2011 10:37:55 -0400
Isn't the 1=1 there because someone doesn't want to use the proper ANSI
syntax?
I would think
SELECT P.last_name
, P.first_name
, s.title
, T.created AS completed
FROM persons P
JOIN required_courses s
ON 1 = 1
...
is better written as
SELECT P.last_name
, P.first_name
, s.title
, T.created AS completed
FROM persons P
CROSS JOIN required_courses s
On Wed, May 4, 2011 at 10:12 AM, Ric Van Dyke <ric.van.dyke@xxxxxxxxxx>wrote:
> I'm pretty sure that 1=1 has never improved performance of a query; it's
> like adding "TURE" to a statement. Certainly since about 9 or so the
> optimizer removes it as a predicate, notice the 1=1 predicate isn't applied
> at all in the plan below (yes I truncated the plan so as to fit better):
>
> SQL> set autotrace traceonly explain
> SQL> select * from emp where 1=1 and deptno = 10;
>
> Execution Plan
> ----------------------------------------------------------
> Plan hash value: 919097248
>
> ------------------------------------------------------------
> | Id | Operation | Name | Rows |
> ------------------------------------------------------------
> | 0 | SELECT STATEMENT | | 4 |
> | 1 | TABLE ACCESS BY INDEX ROWID| EMP | 4 |
> |* 2 | INDEX RANGE SCAN | EMP_DEPT_IDX | 4 |
> ------------------------------------------------------------
>
> Predicate Information (identified by operation id):
> ---------------------------------------------------
>
> 2 - access("DEPTNO"=10)
>
>
> As to the query with an outer join in Oracle syntax:
>
> Think of the + as a grave marker, and think that you need to put the grave
> marker on the side of the query where you need the ghost records from. So
> which table will there not be a match on that you want records from? That
> is the side you put the + on.
>
> I hope that helps.
>
> -----------------------
> Ric Van Dyke
> Hotsos Enterprises
> Cell 248-705-0624
> -----------------------
>
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> 4-8 March 2012 Start making plans now!
>
>
> -----Original Message-----
> From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
> On Behalf Of Amaral, Rui
> Sent: Wednesday, May 04, 2011 9:50 AM
> To: 'rjoralist2@xxxxxxxxxxxxxxxxxxxxx'; oracle-l@xxxxxxxxxxxxx
> Subject: RE: Just as a learning exercise
>
> "1=1" - I seem to remember the same thing (tho not hop-soaked) and
> eventually got phased out as being not helpful at all.
>
>
> Rui Amaral
> Database Administrator
> ITS - SSG
> TD Bank Financial Group
> 220 Bay St., 11th Floor
> Toronto, ON, CA, M5K1A2
> (bb) (647) 204-9106
>
>
> -----Original Message-----
> From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
> On Behalf Of Rich Jesse
> Sent: Wednesday, May 04, 2011 9:44 AM
> To: oracle-l@xxxxxxxxxxxxx
> Subject: Re: Just as a learning exercise
>
> Joe writes:
>
> > to truncate the time component?
>
> ...which not only unnecessary in the comparison, but a performance drain.
> Also, although it defaults to midnight, I'd add the time component in the
> TO_DATE calls.
>
> As far as the "1=1", when I started my current job, consultants used that
> in every statement. A distant hop-soaked memory thinks it was a hack to
> attempt to remind the optimizer that the first table specified in the FROM
> was the driving table (or something like that?) in pre-9i days.
>
> > From:
> > Paul Drake <bdbafh@xxxxxxxxx>
>
> ...
>
> > Why would anyone ever apply a TRUNC ( ) function to a date column in a
> > where clause?
>
> Rich
>
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--
Rumpi Gravenstein
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