Oracle-L: RE: Number of joins in the query

From: DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM>
Date: Thu, 27 Feb 2003 08:04:25 -0800
Message-ID: <F001.0055B993.20030227080425@fatcity.com>

Ranganath

On looking closer at your model, it appears you may have duplicated keys. That may be the source of your confusion. Your model may not be properly normalized. What is the relationship between the three tables? It appears that Station is the parent of the two other tables, but its key is propagated to both of the other two. What is the relation between Station_restriction and Stn_rstcn_to_frm? What is the primary key for Stn_rstcn_to_frm?

Dennis Williams
DBA, 40%OCP, 100% DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
[mailto:Ranganath.Krishnaswamy_at_blr.hpsglobal.com] Sent: Thursday, February 27, 2003 8:59 AM To: Multiple recipients of list ORACLE-L

Dear List,

I have a basic doubt about the number of joins I should have. Say, I have three tables by name station, station_restriction and stn_rstcn_to_frm with the following structure:

Station                Station_restriction             stn_rstcn_to_frm
----------               ----------------------------
-------------------------
stn_key(PK)          stn_rstcn_key(PK)            stn_rstcn_key(FK)
station_code         stn_key(FK)                      stn_key(FK)
station_name        restricted_position              country

	If I have to select data from all the three tables should I have two

joins or three joins?

If I have two joins, I would have

Station.stn_key=Station_restriction.stn_key and Station_restriction.stn_rstcn_key = stn_rstcn_to_frm.stn_rstcn_key.

If I have three joins I would have

Station.stn_key=Station_restriction.stn_key and Station_restriction.stn_rstcn_key = stn_rstcn_to_frm.stn_rstcn_key

and Station.stn_key = stn_rstcn_to_frm.stn_key

Can anybody let me know as to how many joins should I have so that I don't get any cartesian product in the result set?

I am sorry if the question sounds trivial to someone but I got this basic doubt while writing a complex query for a multi-table join.

Any help in this regard is very much appreciated.

Thanks and Regards,

Ranganath

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Author: Krishnaswamy, Ranganath
INET: Ranganath.Krishnaswamy_at_blr.hpsglobal.com

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Author: DENNIS WILLIAMS
INET: DWILLIAMS_at_LIFETOUCH.COM

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