Insert, on duplicate update in PostgreSQL?

Question

Several months ago I learned from an answer on Stack Overflow how to perform multiple updates at once in MySQL using the following syntax:

INSERT INTO table (id, field, field2) VALUES (1, A, X), (2, B, Y), (3, C, Z) ON DUPLICATE KEY UPDATE field=VALUES(Col1), field2=VALUES(Col2); 

I've now switched over to PostgreSQL and apparently this is not correct. It's referring to all the correct tables so I assume it's a matter of different keywords being used but I'm not sure where in the PostgreSQL documentation this is covered.

To clarify, I want to insert several things and if they already exist to update them.

Answer 1

PostgreSQL since version 9.5 has UPSERT syntax, with ON CONFLICT clause. with the following syntax (similar to MySQL)

INSERT INTO the_table (id, column_1, column_2)  VALUES (1, 'A', 'X'), (2, 'B', 'Y'), (3, 'C', 'Z') ON CONFLICT (id) DO UPDATE    SET column_1 = excluded.column_1,        column_2 = excluded.column_2; 

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Searching postgresql's email group archives for "upsert" leads to finding an example of doing what you possibly want to do, in the manual:

Example 38-2. Exceptions with UPDATE/INSERT

This example uses exception handling to perform either UPDATE or INSERT, as appropriate:

CREATE TABLE db (a INT PRIMARY KEY, b TEXT);  CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS $$ BEGIN     LOOP         -- first try to update the key         -- note that "a" must be unique         UPDATE db SET b = data WHERE a = key;         IF found THEN             RETURN;         END IF;         -- not there, so try to insert the key         -- if someone else inserts the same key concurrently,         -- we could get a unique-key failure         BEGIN             INSERT INTO db(a,b) VALUES (key, data);             RETURN;         EXCEPTION WHEN unique_violation THEN             -- do nothing, and loop to try the UPDATE again         END;     END LOOP; END; $$ LANGUAGE plpgsql;  SELECT merge_db(1, 'david'); SELECT merge_db(1, 'dennis'); 

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There's possibly an example of how to do this in bulk, using CTEs in 9.1 and above, in the hackers mailing list:

WITH foos AS (SELECT (UNNEST(%foo[])).*) updated as (UPDATE foo SET foo.a = foos.a ... RETURNING foo.id) INSERT INTO foo SELECT foos.* FROM foos LEFT JOIN updated USING(id) WHERE updated.id IS NULL; 

See a_horse_with_no_name's answer for a clearer example.