On 11/08/2016 12:08 PM, Karl Czajkowski wrote:
Hi,
Is there a formal definition for the order in which constraint actions
(i.e. the ON DELETE or ON UPDATE rules) are applied when there are
multiple overlapping/relevant constraints?
I have struggled to find an answer in the manual, but my experiments
suggest that they are interpreted in the order in which the
constraints were defined and the first rule in this order is applied
while subsequent rules are ignored. This can be very confusing if one
rule says CASCADE and another NO ACTION, and you need to understand
this order of definition to know whether a delete will cascade or
raise an error.
Can you provide an example?
Is there a definitive way to introspect the informatation_schema or
pg_catalog to determine which behaviors will effectively apply to a
given "DELETE FROM ..." or "UPDATE ..." statement?
Just to clear you are talking about FK constraints, correct?
AFAIK they are just a form of trigger and the rules they follow can be
found here:
https://www.postgresql.org/docs/9.5/static/sql-createtrigger.html
"If multiple triggers of the same kind are defined for the same event,
they will be fired in alphabetical order by name."
There is more, so I would read through the whole thing.
Thanks,
Karl
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Adrian Klaver
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