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

From: Saira Somani <saira_somani_at_yahoo.com>
Date: Thu, 27 Feb 2003 08:39:19 -0800
Message-ID: <F001.0055BA7E.20030227083919@fatcity.com>

A joins B joins C

Is the same as A joins C

So I would think 2 joins is all you need - 3 would give you an unnecessary loop...but I could be wrong.

-----Original Message-----
Krishnaswamy, Ranganath
Sent: February 27, 2003 9:59 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: Saira Somani
INET: saira_somani_at_yahoo.com

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