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> 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