No unique or exclusion constraint matching the ON CONFLICT

Solution 1:

Per the docs,

All table_name unique indexes that, without regard to order, contain exactly the conflict_target-specified columns/expressions are inferred (chosen) as arbiter indexes. If an index_predicate is specified, it must, as a further requirement for inference, satisfy arbiter indexes.

The docs go on to say,

[index_predicate are u]sed to allow inference of partial unique indexes

In an understated way, the docs are saying that when using a partial index and upserting with ON CONFLICT, the index_predicate must be specified. It is not inferred for you. I learned this here, and the following example demonstrates this.

CREATE TABLE test.accounts (
    id int PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
    type text,
    person_id int);
CREATE UNIQUE INDEX accounts_note_idx on accounts (type, person_id) WHERE ((type)::text = 'PersonAccount'::text);
INSERT INTO  test.accounts (type, person_id) VALUES ('PersonAccount', 10);

so that we have:

unutbu=# select * from test.accounts;
+----+---------------+-----------+
| id |     type      | person_id |
+----+---------------+-----------+
|  1 | PersonAccount |        10 |
+----+---------------+-----------+
(1 row)

Without index_predicate we get an error:

INSERT INTO  test.accounts (type, person_id) VALUES ('PersonAccount', 10) ON CONFLICT (type, person_id) DO NOTHING;
-- ERROR:  there is no unique or exclusion constraint matching the ON CONFLICT specification

But if instead you include the index_predicate, WHERE ((type)::text = 'PersonAccount'::text):

INSERT INTO  test.accounts (type, person_id) VALUES ('PersonAccount', 10)
ON CONFLICT (type, person_id)
WHERE ((type)::text = 'PersonAccount'::text) DO NOTHING;

then there is no error and DO NOTHING is honored.

Solution 2:

A possible simple solution of this error

First of all let's see the cause of error with a simple example. Here is the table mapping products to categories.

create table if not exists product_categories (
    product_id uuid references products(product_id) not null,
    category_id uuid references categories(category_id) not null,
    whitelist boolean default false
);

If we use this query:

INSERT INTO product_categories (product_id, category_id, whitelist)
VALUES ('123...', '456...', TRUE)
ON CONFLICT (product_id, category_id)
DO UPDATE SET whitelist=EXCLUDED.whitelist;

This will give you error No unique or exclusion constraint matching the ON CONFLICT because there is no unique constraint on product_id and category_id. There could be multiple rows having the same combination of product and category id (so there can never be a conflict on them).

Solution:

Use unique constraint on both product_id and category_id like this:

create table if not exists product_categories (
    product_id uuid references products(product_id) not null,
    category_id uuid references categories(category_id) not null,
    whitelist boolean default false,
    primary key(product_id, category_id) -- This will solve the problem
    -- unique(product_id, category_id) -- OR this if you already have a primary key
);

Now you can use ON CONFLICT (product_id, category_id) for both columns without any error.

In short: Whatever column(s) you use with on conflict, they should have unique constraint.

Solution 3:

The easy way to fix it is by setting the conflicting column as UNIQUE

Solution 4:

I did not have a chance to play with UPSERT, but I think you have a case from docs:

Note that this means a non-partial unique index (a unique index without a predicate) will be inferred (and thus used by ON CONFLICT) if such an index satisfying every other criteria is available. If an attempt at inference is unsuccessful, an error is raised.