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          


        

Answer 1

I was looking for the same thing when I came here, but the lack of a generic "upsert" function botherd me a bit so I thought you could just pass the update and insert sql as arguments on that function form the manual

that would look like this:

CREATE FUNCTION upsert (sql_update TEXT, sql_insert TEXT)
    RETURNS VOID
    LANGUAGE plpgsql
AS $$
BEGIN
    LOOP
        -- first try to update
        EXECUTE sql_update;
        -- check if the row is found
        IF FOUND THEN
            RETURN;
        END IF;
        -- not found so insert the row
        BEGIN
            EXECUTE sql_insert;
            RETURN;
            EXCEPTION WHEN unique_violation THEN
                -- do nothing and loop
        END;
    END LOOP;
END;
$$;

and perhaps to do what you initially wanted to do, batch "upsert", you could use Tcl to split the sql_update and loop the individual updates, the preformance hit will be very small see http://archives.postgresql.org/pgsql-performance/2006-04/msg00557.php

the highest cost is executing the query from your code, on the database side the execution cost is much smaller