Postgres 11

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CREATE TABLE other    (name text PRIMARY KEY, datum date NOT NULL);
INSERT INTO other VALUES ('foo', '2019-1-2');

CREATE TABLE playlist (name text, datum date NOT NULL);

CREATE OR REPLACE FUNCTION trg_cur_date()
  RETURNS TRIGGER AS
$func$
BEGIN
   SELECT o.datum
   FROM   other o
   WHERE  o.name  = NEW.name
   AND    o.datum < NEW.datum

   UNION ALL
   SELECT NEW.datum
   LIMIT  1
   INTO   NEW.datum;

   RETURN NEW;
END
$func$ LANGUAGE plpgsql;

CREATE TRIGGER playlist_ins_bef
BEFORE INSERT ON playlist
FOR EACH ROW EXECUTE PROCEDURE trg_cur_date();
1 rows affected

INSERT INTO playlist VALUES ('foo','2019-1-5') -- bigger date
RETURNING *;


name
datum


foo
2019-01-02


INSERT INTO playlist VALUES ('foo','2019-1-1') -- earlier date
RETURNING *;


name
datum


foo
2019-01-01


INSERT INTO playlist VALUES ('bar','2019-1-7') -- new name (no match)
RETURNING *;


name
datum


bar
2019-01-07