From: | "Brent Wood" <b(dot)wood(at)niwa(dot)co(dot)nz> |
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To: | |
Cc: | <pgsql-general(at)postgresql(dot)org> |
Subject: | Help with a foreign key with non-unique reference? |
Date: | 2008-09-16 03:12:53 |
Message-ID: | 48CFCCF50200007B000155CE@gwia1.ham.niwa.co.nz |
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Lists: | pgsql-general |
Hi,
I need a foreign key (or equivalent) where the referenced table cannot have a unique constraint.
For fisheries surveys we have a table of catch records. For a given event, several species are caught, and are weighed by one or more methods. Thus a given event may have more than one record for the same spaecies, as parts of the catch may be weighed differently.
When we sample a species for measuring, the event is recorded, but as the sample may include individuals from throughout the catch, it does not necessarily relate to the catch-with-method table.
It is possible to have catch/sub-catch tables where the catch table no method & stores the aggregated weight of each sub-catch (with method), but I prefer to avoid this if possible.
How can I impose a constraint on the table of length data, so that the event/species has teh equivalent of a referential on catch(event,species) when I cannot have a unique index on catch(event,species)?
Thanks,
Brent Wood
Brent Wood
DBA/GIS consultant
NIWA, Wellington
New Zealand
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