問題描述:
按照天數統計每天的總數,如果其中有幾天沒有數據,那麼group by 返回會忽略那幾天,不符合報表統計的需求。當天沒有數據的話該如何填充0 ?
數據庫腳本
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for employee
-- ----------------------------
DROP TABLE IF EXISTS `employee`;
CREATE TABLE `employee` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
`age` int(11) NULL DEFAULT NULL,
`sex` char(2) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
`addr` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
`create_time` datetime(0) NULL DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 9 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of employee
-- ----------------------------
INSERT INTO `employee` VALUES (1, 'zhansan', 18, '男', '北京市', '2019-06-13 18:41:34');
INSERT INTO `employee` VALUES (2, 'lisi', 20, '男', '天津市', '2019-06-14 18:41:43');
INSERT INTO `employee` VALUES (3, 'wangwu', 28, '男', '上海', '2019-06-18 18:41:37');
INSERT INTO `employee` VALUES (4, 'lisi', 35, '男', '香港', '2019-06-18 18:41:51');
INSERT INTO `employee` VALUES (5, 'limei', 22, '女', '山西', '2019-06-19 18:41:58');
INSERT INTO `employee` VALUES (6, 'liting', 26, '女', '北京市', '2019-06-21 18:42:03');
INSERT INTO `employee` VALUES (7, 'wangdan', 31, '女', '河北省', '2019-06-19 19:22:31');
INSERT INTO `employee` VALUES (8, 'limeili', 19, '女', '安徽省', '2019-06-19 19:27:45');
SET FOREIGN_KEY_CHECKS = 1;
先看解決方案:
/**
如果使用當前日期的話 ,將'2019-06-22'替換爲CURDATE( )
*/
SELECT
t1.`day`,
COUNT( t2.id ) num
FROM
(
SELECT
@cdate := DATE_ADD( @cdate, INTERVAL - 1 DAY ) DAY
FROM
( SELECT @cdate := DATE_ADD( '2019-06-22', INTERVAL + 1 DAY ) FROM employee ) t0
LIMIT 7
) t1
LEFT JOIN (
SELECT
DATE( a.create_time ) DAY,
a.id
FROM
employee a
WHERE
DATE( create_time ) <= '2019-06-22' AND DATE( create_time ) > DATE_SUB( '2019-06-22', INTERVAL 7 DAY )
) t2 ON t2.DAY = t1.DAY
GROUP BY
t1.`day`;
執行數據結果完全符合需求;
連續日期mysql
/**
如果指定開始日期的話 ,將CURDATE( )替換爲'2019-06-13'
*/
SELECT
@cdate := DATE_ADD( @cdate, INTERVAL - 1 DAY ) DAY
FROM
( SELECT @cdate := DATE_ADD( CURDATE( ), INTERVAL + 1 DAY ) FROM employee ) t0
LIMIT 7;
SQL分析:
1. @cdate := 是定義名爲cdate的變量並賦值(select 後面必須用:=)
2. @cdate := DATE_ADD(CURDATE(), INTERVAL + 1 DAY) 按照當前日期,加一天
3. SELECT @cdate := DATE_ADD(CURDATE(), INTERVAL + 1 DAY) FROM 數據庫表名
4. @cdate := DATE_ADD(@cdate, INTERVAL - 1 DAY) DAY 把定義的cdate變量天數-1(自減)
5. LIMIT 7 限制一下條數,得到了指定日期往前7天的記錄
6. left join group by t1.day 即按照左表關聯業務數據,根據左表的日期分組,即分成了指定的7天數據,有記錄就統計條數,沒有記錄就是0