Use multiple conflict_target in ON CONFLICT clause - postgresql

Question

I have two columns in table col1, col2, they both are unique indexed (col1 is unique and so is col2).
I need at insert into this table, use ON CONFLICT syntax and update other columns, but I can't use both column in conflict_targetclause.
It works:
INSERT INTO table
...
ON CONFLICT ( col1 )
DO UPDATE
SET
-- update needed columns here
But how to do this for several columns, something like this:
...
ON CONFLICT ( col1, col2 )
DO UPDATE
SET
....

Answer 1

ON CONFLICT requires a unique index* to do the conflict detection. So you just need to create a unique index on both columns:
t=# create table t (id integer, a text, b text);
CREATE TABLE
t=# create unique index idx_t_id_a on t (id, a);
CREATE INDEX
t=# insert into t values (1, 'a', 'foo');
INSERT 0 1
t=# insert into t values (1, 'a', 'bar') on conflict (id, a) do update set b = 'bar';
INSERT 0 1
t=# select * from t;
id | a | b
----+---+-----
1 | a | bar
* In addition to unique indexes, you can also use exclusion constraints. These are a bit more general than unique constraints. Suppose your table had columns for id and valid_time (and valid_time is a tsrange), and you wanted to allow duplicate ids, but not for overlapping time periods. A unique constraint won't help you, but with an exclusion constraint you can say "exclude new records if their id equals an old id and also their valid_time overlaps its valid_time."

Answer 2

A sample table and data
CREATE TABLE dupes(col1 int primary key, col2 int, col3 text,
CONSTRAINT col2_unique UNIQUE (col2)
);
INSERT INTO dupes values(1,1,'a'),(2,2,'b');
Reproducing the problem
INSERT INTO dupes values(3,2,'c')
ON CONFLICT (col1) DO UPDATE SET col3 = 'c', col2 = 2
Let's call this Q1. The result is
ERROR: duplicate key value violates unique constraint "col2_unique"
DETAIL: Key (col2)=(2) already exists.
What the documentation says
conflict_target can perform unique index inference. When performing
inference, it consists of one or more index_column_name columns and/or
index_expression expressions, and an optional index_predicate. 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.
This gives the impression that the following query should work, but it does not because it would actually require a together unique index on col1 and col2. However such an index would not guarantee that col1 and col2 would be unique individually which is one of the OP's requirements.
INSERT INTO dupes values(3,2,'c')
ON CONFLICT (col1,col2) DO UPDATE SET col3 = 'c', col2 = 2
Let's call this query Q2 (this fails with a syntax error)
Why?
Postgresql behaves this way is because what should happen when a conflict occurs on the second column is not well defined. There are number of possibilities. For example in the above Q1 query, should postgresql update col1 when there is a conflict on col2? But what if that leads to another conflict on col1? how is postgresql expected to handle that?
A solution
A solution is to combine ON CONFLICT with old fashioned UPSERT.
CREATE OR REPLACE FUNCTION merge_db(key1 INT, key2 INT, data TEXT) RETURNS VOID AS
$$
BEGIN
LOOP
-- first try to update the key
UPDATE dupes SET col3 = data WHERE col1 = key1 and col2 = key2;
IF found THEN
RETURN;
END IF;
-- not there, so try to insert the key
-- if someone else inserts the same key concurrently, or key2
-- already exists in col2,
-- we could get a unique-key failure
BEGIN
INSERT INTO dupes VALUES (key1, key2, data) ON CONFLICT (col1) DO UPDATE SET col3 = data;
RETURN;
EXCEPTION WHEN unique_violation THEN
BEGIN
INSERT INTO dupes VALUES (key1, key2, data) ON CONFLICT (col2) DO UPDATE SET col3 = data;
RETURN;
EXCEPTION WHEN unique_violation THEN
-- Do nothing, and loop to try the UPDATE again.
END;
END;
END LOOP;
END;
$$
LANGUAGE plpgsql;
You would need to modify the logic of this stored function so that it updates the columns exactly the way you want it to. Invoke it like
SELECT merge_db(3,2,'c');
SELECT merge_db(1,2,'d');

Answer 3

In nowadays is (seems) impossible. Neither the last version of the ON CONFLICT syntax permits to repeat the clause, nor with CTE is possible: not is possible to breack the INSERT from ON CONFLICT to add more conflict-targets.

Answer 4

If you are using postgres 9.5, you can use the EXCLUDED space.
Example taken from What's new in PostgreSQL 9.5:
INSERT INTO user_logins (username, logins)
VALUES ('Naomi',1),('James',1)
ON CONFLICT (username)
DO UPDATE SET logins = user_logins.logins + EXCLUDED.logins;

Answer 5

Vlad got the right idea.
First you have to create a table unique constraint on the columns col1, col2 Then once you do that you can do the following:
INSERT INTO dupes values(3,2,'c')
ON CONFLICT ON CONSTRAINT dupes_pkey
DO UPDATE SET col3 = 'c', col2 = 2

Answer 6

ON CONFLICT ( col1, col2 )
DO UPDATE
SET
works fine. but you should not update col1, col2 in the SET section.

Answer 7

Create a constraint (foreign index, for example).
OR/AND
Look at existing constraints (\d in psq).
Use ON CONSTRAINT(constraint_name) in the INSERT clause.

Answer 8

You can typically (I would think) generate a statement with only one on conflict that specifies the one and only constraint that is of relevance, for the thing you are inserting.
Because typically, only one constraint is the "relevant" one, at a time. (If many, then I'm wondering if something is weird / oddly-designed, hmm.)
Example:
(License: Not CC0, only CC-By)
// there're these unique constraints:
// unique (site_id, people_id, page_id)
// unique (site_id, people_id, pages_in_whole_site)
// unique (site_id, people_id, pages_in_category_id)
// and only *one* of page-id, category-id, whole-site-true/false
// can be specified. So only one constraint is "active", at a time.
val thingColumnName = thingColumnName(notfificationPreference)
val insertStatement = s"""
insert into page_notf_prefs (
site_id,
people_id,
notf_level,
page_id,
pages_in_whole_site,
pages_in_category_id)
values (?, ?, ?, ?, ?, ?)
-- There can be only one on-conflict clause.
on conflict (site_id, people_id, $thingColumnName) <—— look
do update set
notf_level = excluded.notf_level
"""
val values = List(
siteId.asAnyRef,
notfPref.peopleId.asAnyRef,
notfPref.notfLevel.toInt.asAnyRef,
// Only one of these is non-null:
notfPref.pageId.orNullVarchar,
if (notfPref.wholeSite) true.asAnyRef else NullBoolean,
notfPref.pagesInCategoryId.orNullInt)
runUpdateSingleRow(insertStatement, values)
And:
private def thingColumnName(notfPref: PageNotfPref): String =
if (notfPref.pageId.isDefined)
"page_id"
else if (notfPref.pagesInCategoryId.isDefined)
"pages_in_category_id"
else if (notfPref.wholeSite)
"pages_in_whole_site"
else
die("TyE2ABK057")
The on conflict clause is dynamically generated, depending on what I'm trying to do. If I'm inserting a notification preference, for a page — then there can be a unique conflict, on the site_id, people_id, page_id constraint. And if I'm configuring notification prefs, for a category — then instead I know that the constraint that can get violated, is site_id, people_id, category_id.
So I can, and fairly likely you too, in your case?, generate the correct on conflict (... columns ), because I know what I want to do, and then I know which single one of the many unique constraints, is the one that can get violated.

Answer 9

Kind of hacky but I solved this by concatenating the two values from col1 and col2 into a new column, col3 (kind of like an index of the two) and compared against that. This only works if you need it to match BOTH col1 and col2.
INSERT INTO table
...
ON CONFLICT ( col3 )
DO UPDATE
SET
-- update needed columns here
Where col3 = the concatenation of the values from col1 and col2.

Answer 10

I get I am late to the party but for the people looking for answers I found this:
here
INSERT INTO tbl_Employee
VALUES (6,'Noor')
ON CONFLICT (EmpID,EmpName)
DO NOTHING;

Answer 11

ON CONFLICT is very clumsy solution, run
UPDATE dupes SET key1=$1, key2=$2 where key3=$3
if rowcount > 0
INSERT dupes (key1, key2, key3) values ($1,$2,$3);
works on Oracle, Postgres and all other database