Re: AFTER INSERT trigger INSERT into another table-B are ignoring Table-B constraints

Hi Rui,

I appreciate your response on this.
I am in the scenario of using x_idx1 but with I am going thru constraints. I am not using indexes.

Constraints are working as expected when I am working the table-2 directly.
In my case, Table-2 needs to get INSERTed only when table-1 has INSERTs. Table-1 is working fine. Table-2 is also working fine when I am directly working in table-2.
But when I Table-2 needs to have INSERTs based on the trigger invocation of Table-1, Table-2 is applying constraints which is causing issues.

Thanks,
Sarwar

________________________________
From: Rui DeSousa <rui(dot)desousa(at)icloud(dot)com>
Sent: Wednesday, May 22, 2024 10:42 PM
To: M Sarwar <sarwarmd02(at)outlook(dot)com>
Cc: David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>; wolters(dot)k(at)web(dot)de <wolters(dot)k(at)web(dot)de>; pgsql-admin(at)lists(dot)postgresql(dot)org <pgsql-admin(at)lists(dot)postgresql(dot)org>
Subject: Re: AFTER INSERT trigger INSERT into another table-B are ignoring Table-B constraints

On May 22, 2024, at 9:22 PM, M Sarwar <sarwarmd02(at)outlook(dot)com<mailto:sarwarmd02(at)outlook(dot)com>> wrote:

Hi David,
I did verify at Ver 13 and this ( UNIQUE NULLS NOT DISTINCT ) syntax is not existing there. That means, I need to work on it without this option.
My team will not upgrade from 13 due to number of reasons.

In that case you could use a functional unique index with a digest to teat nulls as not distinct instead; although I do prefer NULL to be distinct. To me this indicates that the schema is not fully normalized and/or ported from MS SQL server.

I’ve used this approach when dealing with organic schemas that had simular logic and requirements.

x_idx1 — is to fulfill queries and traditional unique values. (Better to use a constraint instead for correctness/readability)
x_idx2 — handles uniqueness when one of values is null. (Must be an index as constraints do not support functional indexes)

prod=> \d x
Table "rui.x"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+---------
a | integer | | |
b | integer | | |
c | integer | | |
Indexes:
"x_idx1" UNIQUE, btree (a, b, c)
"x_idx2" UNIQUE, btree (pgcrypto.digest((COALESCE(a::text, '<null>'::text) || COALESCE(b::text, '<null>'::text)) || COALESCE(c::text, '<null>'::text), 'sha256'::text)) WHERE a IS NULL OR b IS NULL OR c IS NULL

prod=> insert into x values (1, 2, null);
INSERT 0 1
Time: 1.741 ms
prod=> insert into x values (1, 2, null);
ERROR: duplicate key value violates unique constraint "x_idx2"
DETAIL: Key (pgcrypto.digest((COALESCE(a::text, '<null>'::text) || COALESCE(b::text, '<null>'::text)) || COALESCE(c::text, '<null>'::text), 'sha256'::text))=(\x7cce718aefddfbd5db7925f15b0ab319d7f06b4aeae096a1542f8d1adeef36be) already exists.
Time: 0.843 ms
prod=> insert into x values (2, 2, 2);
INSERT 0 1
Time: 2.451 ms
prod=> insert into x values (2, 2, 2);
ERROR: duplicate key value violates unique constraint "x_idx1"
DETAIL: Key (a, b, c)=(2, 2, 2) already exists.
Time: 0.698 ms