1、表结构
CREATE TABLE `ringratio` (
`id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键id，自增',
`num` int(11) NOT NULL COMMENT '具体数据',
`year` smallint(6) NOT NULL COMMENT '年份',
`month` smallint(5) unsigned NOT NULL COMMENT '月份',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='环比实现表';
2、其中数据（包括13个月，为了演示跨年的时候计算）
insert into ringratio (id, num, year, month) values (1, 100, 2017, 1);
insert into ringratio (id, num, year, month) values (2, 130, 2017, 2);
insert into ringratio (id, num, year, month) values (3, 110, 2017, 3);
insert into ringratio (id, num, year, month) values (4, 90, 2017, 4);
insert into ringratio (id, num, year, month) values (5, 150, 2017, 5);
insert into ringratio (id, num, year, month) values (6, 190, 2017, 6);
insert into ringratio (id, num, year, month) values (7, 210, 2017, 7);
insert into ringratio (id, num, year, month) values (8, 120, 2017, 8);
insert into ringratio (id, num, year, month) values (9, 130, 2017, 9);
insert into ringratio (id, num, year, month) values (10, 180, 2017, 10);
insert into ringratio (id, num, year, month) values (11, 110, 2017, 11);
insert into ringratio (id, num, year, month) values (12, 220, 2017, 12);
insert into ringratio (id, num, year, month) values (13, 330, 2018, 1);
3、查询sql
select ( thismonth.num-lastmonth.num)/lastmonth.num '环比增长' ,thismonth.year ‘年’,thismonth.month ‘月’
from ringratio thismonth,ringratio lastmonth
where
case when thismonth.month >1 then thismonth.year=lastmonth.year and thismonth.month = lastmonth.month+1
when thismonth.month = 1 then thismonth.year=lastmonth.year+1 and lastmonth.month=12 end
简单说明
就是本月数据和前一个月的数据作为两个表进行内连接，之后进行查询
本sql适合在数据量较小的表（如数据中间表、汇总表）中进行查询
