可以使用 Trigger,新增 A table 時就會去 update B table 了,以下用 Postgresql 資料庫為例

<pre class="c" name="code">
CREATE TABLE A (
  id character(15) NOT NULL primary key,
  quantity integer
);

CREATE TABLE B (
  id character(15) NOT NULL primary key,
  quantity integer
);


CREATE OR REPLACE FUNCTION addOtherTableQuantity() RETURNS trigger AS '
DECLARE
  changed boolean;
BEGIN
  UPDATE B SET quantity = (new.quantity + quantity) where id = new.id; 
  RETURN new;
END
' LANGUAGE plpgsql;


CREATE TRIGGER add_Other_Table_Quantity AFTER INSERT ON A
  FOR EACH ROW EXECUTE PROCEDURE addOtherTableQuantity();

insert into B  VALUES('1',5);
insert into A  VALUES('1',5);

SELECT * FROM B;

當然也可用 PHP,把以下的 SQL 包在同一個 Transaction 即可

<pre class="c" name="code">
insert into A  VALUES('1',5);
UPDATE B SET quantity = (5 + quantity) where id = 1;