我就廢話不多說了,大家還是直接看代碼吧~
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
補充:MySQL一條SQL語句查詢多條統計結果
商城項目難免會遇到使用者個人中心頁查詢不同狀态訂單數量的問題。當然這個問題并不難,可以寫一個DAO層方法,以狀态作為入參,每次傳入不同狀态值依次查詢相應狀态的訂單數量。
今天在寫H5端接口時,我想換種方式查,也就是通過一條SQL查詢出多個狀态的訂單數量。在網上搜了搜,方法可行,是以就嘗試了下,果不其然成功了。
示例如下(資料隻為示範今天的問題,表設計并不嚴謹。勿怪):
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 '訂單号',
`user_id` int(11) DEFAULT NULL COMMENT '使用者id',
`shop_id` int(11) DEFAULT NULL COMMENT '商家id',
`order_status` tinyint(1) DEFAULT NULL COMMENT '訂單狀态',
`create_time` int(10) DEFAULT NULL COMMENT '建立時間',
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', 'cccccccccc', '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');
核心SQL語句如下:
SELECT COUNT(CASE order_status WHEN 1 THEN 1 END) AS "狀态1",COUNT(CASE order_status WHEN 2 THEN 1 END) AS "狀态2",COUNT(CASE order_status WHEN 3 THEN 1 END) AS "狀态3",COUNT(CASE order_status WHEN 4 THEN 1 END) AS "狀态4" FROM `mini_test_order`;
或如下:
SELECT COUNT(CASE WHEN order_status = 1 THEN 1 END) AS "狀态1",COUNT(CASE WHEN order_status = 2 THEN 1 END) AS "狀态2",COUNT(CASE WHEN order_status = 3 THEN 1 END) AS "狀态3",COUNT(CASE WHEN order_status = 4 THEN 1 END) AS "狀态4" FROM `mini_test_order` ;
當然,SQL語句不僅僅局限于上述兩種寫法,喜歡探究的童靴歡迎留言補充。
MySQL的case when的文法有兩種
1.簡單函數
CASE [col_name] WHEN [value1] THEN [result1]…ELSE [default] END
2.搜尋函數
CASE WHEN [expr] THEN [result1]…ELSE [default] END
兩者差別
前者枚舉col_name這個字段值為符合條件value1時所有可能的值;
後者可以寫判斷,并且搜尋函數隻會傳回第一個符合條件的值,其他case被忽略。
以上為個人經驗,希望能給大家一個參考,也希望大家多多支援腳本之家。如有錯誤或未考慮完全的地方,望不吝賜教。