Search Postgresql Archives

Re: CANNOT USE ANY INDEX ON UPSERT (INSERT.....ON CONFLICT)

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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 <agharta82@xxxxxxxxx> 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
--
If you can't see the forest for the trees,
cut the trees and you'll find there is no forest.





--
Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general



[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Postgresql Jobs]     [Postgresql Admin]     [Postgresql Performance]     [Linux Clusters]     [PHP Home]     [PHP on Windows]     [Kernel Newbies]     [PHP Classes]     [PHP Books]     [PHP Databases]     [Postgresql & PHP]     [Yosemite]
  Powered by Linux