Postgres 10

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CREATE TABLE psy_revenues
    ("id" int, "owner_id" int, "January" int, "February" int, "March" int, "April" int, "December" int)
;
    
INSERT INTO psy_revenues
    ("id", "owner_id", "January", "February", "March", "April", "December")
VALUES
    (2, 1, 0, 0, 0, 0, 1)
;
1 rows affected

CREATE TABLE psy_consultations
    ("id" int, "first_name" varchar(6), "last_name" varchar(8), "date" timestamp, "payed" int, "owner_id" int)
;
    
INSERT INTO psy_consultations
    ("id", "first_name", "last_name", "date", "payed", "owner_id")
VALUES
    (3, 'Gérard', 'Bouchard', '2018-12-05 09:19:26', 80, 1),
    (4, 'Pasti', 'Lami', '2018-12-06 03:53:52', 60, 2)
;
2 rows affected

CREATE OR REPLACE FUNCTION update_revenues()
RETURNS trigger AS
$BODY$
    DECLARE 
    BEGIN
        EXECUTE format (
            'UPDATE psy_revenues 
              SET  %I = (
                SELECT SUM(payed) FROM psy_consultations WHERE 
                    owner_id =  $1 AND to_char(date, ''MM-YYYY'') = $2 
                    )'
             ,TRIM(to_char(NEW.date, 'Month')) )      --column name to update(%I)
 USING NEW.owner_id , to_char(NEW.date, 'MM-YYYY');--values for owner_id & month
    RETURN NEW;
    END;
$BODY$ LANGUAGE plpgsql;
CREATE TRIGGER update_revenues
AFTER INSERT 
ON psy_consultations
FOR EACH ROW 
EXECUTE PROCEDURE update_revenues();
INSERT INTO psy_consultations ("id", "first_name", "last_name", "date", "payed", "owner_id")
VALUES(1,'John','Doe', clock_timestamp(),100,1);
ERROR:  column "September" of relation "psy_revenues" does not exist
LINE 2:               SET  "September" = (
                           ^
QUERY:  UPDATE psy_revenues 
              SET  "September" = (
                SELECT SUM(payed) FROM psy_consultations WHERE 
                    owner_id =  $1 AND to_char(date, 'MM-YYYY') = $2 
                    )
CONTEXT:  PL/pgSQL function update_revenues() line 4 at EXECUTE


select * from psy_revenues;


id
owner_id
January
February
March
April
December


2
1
0
0
0
0
1