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

From: <Sunil_Nookala_at_Dell.com>
Date: Thu, 27 Feb 2003 10:06:22 -0800
Message-ID: <F001.0055BCBE.20030227100622@fatcity.com>

If you are joining 'n' number of tables, you should have a minimum of 'n-1' joining conditions, otherwise it might result in cartesian product.

Sunil Nookala
Dell Corp.

-----Original Message-----
Sent: Thursday, February 27, 2003 10:29 AM To: Multiple recipients of list ORACLE-L

Two!

PK on stn_rstcn_to_frm?

T'would be clearer if you presented your problem as tables a, b, c, rather than getting us to struggle through all these stns...

peter

-----Original Message-----
[mailto:Ranganath.Krishnaswamy_at_blr.hpsglobal.com] Sent: 27 February 2003 14:59
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: Robson, Peter
INET: pgro_at_bgs.ac.uk

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Author:
INET: Sunil_Nookala_at_Dell.com

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