[postgresql] Postgresql, update if row with some unique value exists, else insert

I have a URLs table. They contain

(id int primary key, url character varying unique, content character varying, last analyzed date).

I want to create trigger or something(rule may be), so each time i make insert from my java program, it updates some single row if row with such URL exists. Else it should perform an Insert.

Please, can you provide a complete code in Postgresql. Thanks.

Firstly It tries insert. If there is a conflict on url column then it updates content and last_analyzed fields. If updates are rare this might be better option.

INSERT INTO URLs (url, content, last_analyzed)
VALUES
    (
        %(url)s,
        %(content)s,
        NOW()
    ) 
ON CONFLICT (url) 
DO
UPDATE
SET content=%(content)s, last_analyzed = NOW();

If INSERTS are rare, I would avoid doing a NOT EXISTS (...) since it emits a SELECT on all updates. Instead, take a look at wildpeaks answer: https://dba.stackexchange.com/questions/5815/how-can-i-insert-if-key-not-exist-with-postgresql

CREATE OR REPLACE FUNCTION upsert_tableName(arg1 type, arg2 type) RETURNS VOID AS $$ 
    DECLARE 
    BEGIN 
        UPDATE tableName SET col1 = value WHERE colX = arg1 and colY = arg2; 
        IF NOT FOUND THEN 
        INSERT INTO tableName values (value, arg1, arg2); 
        END IF; 
    END; 
    $$ LANGUAGE 'plpgsql'; 

This way Postgres will initially try to do a UPDATE. If no rows was affected, it will fall back to emitting an INSERT.

I found this post more relevant in this scenario:

WITH upsert AS (
     UPDATE spider_count SET tally=tally+1 
     WHERE date='today' AND spider='Googlebot' 
     RETURNING *
)
INSERT INTO spider_count (spider, tally) 
SELECT 'Googlebot', 1 
WHERE NOT EXISTS (SELECT * FROM upsert)