Beefy Boxes and Bandwidth Generously Provided by pair Networks
Think about Loose Coupling
 
PerlMonks  

Re: Re: Re: SQL JOINs vs WHERE statements

by EdwardG (Vicar)
on Aug 19, 2003 at 19:28 UTC ( [id://284995]=note: print w/replies, xml ) Need Help??


in reply to Re: Re: SQL JOINs vs WHERE statements
in thread SQL JOINs vs WHERE statements

I agree about the named columns, normally insist on them when reviewing, but that piece of code wasn't the pertinent part of the demonstration, just the setup. Thanks though.

Oh, and I used MS SQL Server to test that code. Looks like there's also a portability issue :)

Replies are listed 'Best First'.
Re: Re: Re: Re: SQL JOINs vs WHERE statements
by bean (Monk) on Aug 19, 2003 at 20:57 UTC
    I figured you knew about naming columns when inserting, I just wanted it in the record for any SQL newbies out there.

    I guess to be completely clear and sure of your results, you'd have to do the following to be equivalent to the left outer join version (in MS SQL Server at least):
    SELECT pt.surname, pt.town FROM ( select people.surname, town.town from people, town where people.person_id = town.person_id (+) ) pt WHERE pt.town <> 'Washington' AND pt.town IS NOT NULL
    I just realized that although you've requested a left outer join, what you get is the same as an inner join because all of the columns in your example match up. You need to add a person who isn't in the town table at all:
    insert into people ( person_id, surname ) values ( 5, 'Drifter' )
    What really surprised me was that you got Jones in the results - it seems like MS SQL Server did this:
    SELECT people.surname, t1.town FROM ( select * from town where town <> 'Washington' AND town IS NOT NULL ) t1, people WHERE people.person_id = t1.person_id (+)
    Essentially, it pared down the town table before joining - probably good for performance, although it gives strange results. Interesting - you learn something new every day here at sqlMonks. What? This is perlMonks?
    Update
    That part about it not being an inner join instead of a left outer join? Forget about it - it is a left outer join because of MS SQL Server's apparent order of operations (see my last SQL snippet above).

Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://284995]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this?Last hourOther CB clients
Other Users?
Others lurking in the Monastery: (4)
As of 2024-03-28 13:48 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found