Hi,
Thank you for your suggestion, i'll try to implement it.
Many thanks,
Cheers,
Agharta
Il 18/04/2017 12:38, Alban Hertroys ha scritto:
On 18 Apr 2017, at 10:13, agharta <aghart...@gmail.com> wrote:
Hi all,
I have a problem with INSERT ... ON CONFLICT sql command.
Reading 9.6 documentation i see that ON CONFLICT command will accpets only
index_column_name or index_expression (unique composite/primary indexes are
valid too).
So, my problem is that i can't create any type of upsert-valid index . Let me
explain.
I have a table T1 containing F1, F2, F3, F4 fields.
I can insert same records in T1, MAX TWICE.
How is UPSERT supposed to know which of a pair of duplicate records it is
supposed to update? You'll have to make them unique somehow. The safest
approach is usually to add a surrogate key based on a sequence.
I can have records like (A,B,C,D),(B,A,D,C), etc.. and (A,B,C,D) AGAIN. Any
other next insert of (A,B,C,D) is not allowed (actually it is avoided by a
complex-and-slow-performance select count in before insert/update trigger).
You're probably better off with an EXISTS query there. Something like:
select F1, F2, F3, F4,
case
when exists (select 1 from T1 t where t.F1 = T1.F1 and t.F2 = T1.F2 and t.F3
= T1.F3 and t.F4 = T1.F4 and t.pk <> T1.pk) then 1
else 0
end as have_duplicate
from T1
where F1 = NEW.F1 and F2 = NEW.F2 and F3 = NEW.F3 and F4 = NEW.F4
limit 1;
The pk field in there is the surrogate key from the previous paragraph.
Alternatively, wrap your COUNT around a sub-query that's limited to 2 results.
No extra pk needed in that case, unless you still need to use UPSERT with that.
In either case it will make a big difference to have an index on at least (F1,
F2, F3, F4), perhaps with the new pk column added at the end.
In this case i can't create any type of primary/unique index, like a composite
F1,F2, F3, F4 index. (correct me if i am wrong please).
Correct, you'll most likely have to add a new one (unless someone comes up with
better suggestions).
Alban Hertroys
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cut the trees and you'll find there is no forest.
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