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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