INSERT INTO test.purchase(
	import_id, product_id, usd_price, qty)
	VALUES (2, 'CG-003', 40, 40);

INSERT 0 1
    Query
    returned successfully in 242 msec.

| import_id | product_id | usd_price | euro_price | qty |
|-----------|------------|-----------|------------|-----|
|     2     |  CG-003    |     33    |     33     |  40 |

| product_id | stock_qty | stock_price | stock_amount |
|------------|-----------|-------------|--------------|
|  CG-003    |   null    |    null     |     null     |

     CREATE TABLE test.purchase
    (
        import_id integer NOT NULL,
        product_id text COLLATE pg_catalog."default",
        usd_price numeric(10,2),
        euro_price numeric(10,2),
        qty integer
    )
    
    CREATE TRIGGER tr_p
        AFTER INSERT OR UPDATE OF usd_price
        ON test.purchase
        FOR EACH ROW
        EXECUTE PROCEDURE test.f_conv();

    CREATE FUNCTION test.f_conv()
        RETURNS trigger
        LANGUAGE 'plpgsql'
        COST 100
        VOLATILE NOT LEAKPROOF
    AS $BODY$
    BEGIN
    UPDATE test.purchase pr
    SET euro_price = usd_price / i.rate
    FROM  test.imports i
    WHERE pr.import_id = i.import_id;
    RETURN NEW;
    END
    
    CREATE TRIGGER tr_stock_plus
    AFTER INSERT
    ON test.purchase
    FOR EACH ROW
    EXECUTE PROCEDURE test.f_stock_plus();

    CREATE FUNCTION test.f_stock_plus()
    RETURNS trigger
    LANGUAGE 'plpgsql'
    COST 100
    VOLATILE NOT LEAKPROOF
    AS $BODY$
    BEGIN
    UPDATE test.stock s
    SET stock_qty = stock_qty + 
    (SELECT pr.qty
    FROM test.purchase pr	
    WHERE pr.product_id = s.product_id);
    RETURN NEW;
    END

    CREATE TABLE test.stock
    (
        product_id text COLLATE pg_catalog."default" NOT NULL,
        stock_qty numeric(10,0),
        stock_price numeric(10,2),
        stock_amt numeric(10,2),
        CONSTRAINT stock_pkey PRIMARY KEY (product_id)
    )