常用sql

SELECT 
    year, 
    (SELECT SUM(t2.salary) from t_year t2 where t1.year >= t2.year) salary 
FROM t_year t1;

DROP TABLE IF EXISTS t_product;
CREATE TABLE t_product (
  p_no int(11) NOT NULL COMMENT '编号',
  p_io smallint(1) NOT NULL COMMENT '1：入仓；2：出仓',
  amount int(11) NOT NULL COMMENT '数量'
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

select p_no,IFNULL(sum(case when p_io=1 then amount end)-sum(case when p_io=2 then amount end),sum(case when p_io=1 then amount end)) from t_p group by p_no

SELECT a.p_no, IFNULL(a.c - b.c,a.c) from 
(select p_no, SUM(amount) c from t_p p where p.p_io = 1 GROUP BY p.p_no) a
LEFT JOIN
(select p_no, SUM(amount) c from t_p p where p.p_io = 2 GROUP BY p.p_no) b
on a.p_no = b.p_no

SELECT
  SUM(CASE p_io WHEN 1 THEN   quantity ELSE 0 END) - SUM(CASE p_io WHEN 2 THEN quantity ELSE 0 END)
FROM
    t_product
GROUP BY
   p_no;