环比求助

[ccdbg]

DROP TABLE IF EXISTS `itest`;
CREATE TABLE `itest`  (
  `date` date NOT NULL,
  `num` int(11) DEFAULT NULL,
  PRIMARY KEY (`date`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;

-- ----------------------------
-- Records of itest
-- ----------------------------
INSERT INTO `itest` VALUES ('2018-02-01', 100);
INSERT INTO `itest` VALUES ('2018-02-02', 0);
INSERT INTO `itest` VALUES ('2018-02-03', 0);
INSERT INTO `itest` VALUES ('2018-02-04', 90);
INSERT INTO `itest` VALUES ('2018-02-05', 95);
INSERT INTO `itest` VALUES ('2018-02-06', 0);
INSERT INTO `itest` VALUES ('2018-02-07', 80);

数据示例如上，我想按日期顺序（忽略num为0的日期）求出 90/100, 95/90,80/95，谢谢高人们
希望能写成sql语句，不要搞成函数。。。

[ccdbg]

除了感谢+崇拜啥也不说了

[ACMAIN_CHM]

select a.`date`, a.`num`/(select `num` from itest where `date`<a.`date` and `num`>0 order by `date` desc limit 1) from itest a where num!=0