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

> On 18 Apr 2017, at 10:13, agharta <agharta82@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
(uniquecomposite/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
uniquesomehow. 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
youstill 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
columnadded 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
amwrong 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.