mySql关于统计数量的SQL查询操作

select project_no,
sum(case when device_state=0 then 1 else 0 end)as offTotal ,
sum(case when device_state=1 then 1 else 0 end)as onlineTotal,
sum(1)total
from iot_d_device
group by project_no
order by project_no 

SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for mini_test_order
-- ----------------------------
DROP TABLE IF EXISTS `mini_test_order`;
CREATE TABLE `mini_test_order` (
 `id` int(11) NOT NULL,
 `order_no` varchar(32) DEFAULT NULL COMMENT '订单号',
 `user_id` int(11) DEFAULT NULL COMMENT '用户id',
 `shop_id` int(11) DEFAULT NULL COMMENT '商家id',
 `order_status` tinyint(1) DEFAULT NULL COMMENT '订单状态',
 `create_time` int(10) DEFAULT NULL COMMENT '创建时间',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of mini_test_order
-- ----------------------------
INSERT INTO `mini_test_order` VALUES ('1', 'aaaaaaaaa', '11', '111', '1', '1573041313');
INSERT INTO `mini_test_order` VALUES ('2', 'bbbbbbbb', '11', '222', '1', '1573041313');
INSERT INTO `mini_test_order` VALUES ('3', '', '11', '333', '2', '1573041313');
INSERT INTO `mini_test_order` VALUES ('4', 'dddddddd', '11', '222', '3', '1573041313');
INSERT INTO `mini_test_order` VALUES ('5', 'eeeeeeeee', '11', '111', '4', '1573041313');
INSERT INTO `mini_test_order` VALUES ('6', 'ffffffffffffff', '11', '111', '3', '1573041313');
INSERT INTO `mini_test_order` VALUES ('7', 'gggggggg', '11', '222', '4', '1573041313');
INSERT INTO `mini_test_order` VALUES ('8', 'hhhhhhhhh', '11', '111', '4', '1573041313');
INSERT INTO `mini_test_order` VALUES ('9', 'iiiiiiiiiiiiiiiiiii', '11', '333', '3', '1573041313');
INSERT INTO `mini_test_order` VALUES ('10', 'jjjjjjjjjjjjjjjjjj', '11', '222', '1', '1573041313');

SELECT COUNT(CASE order_status WHEN 1 THEN 1 END) AS "状态1",COUNT(CASE order_status WHEN 2 THEN 1 END) AS "状态2",COUNT(CASE order_status WHEN 3 THEN 1 END) AS "状态3",COUNT(CASE order_status WHEN 4 THEN 1 END) AS "状态4" FROM `mini_test_order`;

SELECT COUNT(CASE WHEN order_status = 1 THEN 1 END) AS "状态1",COUNT(CASE WHEN order_status = 2 THEN 1 END) AS "状态2",COUNT(CASE WHEN order_status = 3 THEN 1 END) AS "状态3",COUNT(CASE WHEN order_status = 4 THEN 1 END) AS "状态4" FROM `mini_test_order` ;

CASE [col_name] WHEN [value1] THEN [result1]…ELSE [default] END

CASE WHEN [expr] THEN [result1]…ELSE [default] END