Mysql 使用联接查询检索记录
我想每天从Mysql 使用联接查询检索记录,mysql,sql,Mysql,Sql,我想每天从emp\u info表中检索上一周的数据 所以我用了: SELECT DAYNAME(timestamp), COUNT(*) FROM `emp_info` WHERE DATE(timestamp ) > DATE_SUB(CURDATE( ) , INTERVAL 1 WEEK ) GROUP BY DAYNAME(timestamp); 根据查询,我得到的结果如下: Monday 5 Thursday 7 但是我也希望工作日的结果为0,没有输入任何记录
emp\u info
表中检索上一周的数据
所以我用了:
SELECT DAYNAME(timestamp), COUNT(*)
FROM `emp_info`
WHERE DATE(timestamp ) > DATE_SUB(CURDATE( ) , INTERVAL 1 WEEK )
GROUP BY DAYNAME(timestamp);
根据查询,我得到的结果如下:
Monday 5
Thursday 7
但是我也希望工作日的结果为0,没有输入任何记录
通过建议,我了解了加入查询。因此,我尝试修复它,但没有得到任何解决方案。您得到的结果是正确的,因为在特定的dayname上没有记录。因为您想要获得所有的日名,所以需要投影一组完整的日(在子查询中使用UNION),并将其与现有查询连接起来
SELECT a.day_name,
COALESCE(b.totalCount, 0) totalCount
FROM
(
SELECT 'Sunday' day_name, 1 ordby UNION ALL
SELECT 'Monday' day_name, 2 ordby UNION ALL
SELECT 'Tuesday' day_name, 3 ordby UNION ALL
SELECT 'Wednesday' day_name, 4 ordby UNION ALL
SELECT 'Thursday' day_name, 5 ordby UNION ALL
SELECT 'Friday' day_name, 6 ordby UNION ALL
SELECT 'Saturday' day_name, 7 ordby
) a
LEFT JOIN
(
SELECT DAYNAME(timestamp) day_name,
COUNT(*) totalCount
FROM `emp_info`
WHERE DATE(timestamp ) > DATE_SUB(CURDATE( ) , INTERVAL 1 WEEK )
GROUP BY DAYNAME(timestamp)
) b ON a.day_name = b.day_name
ORDER BY a.ordby
SELECT a.day_name,
COALESCE(b.totalCount, 0) totalCount
FROM
(
SELECT 'Sunday' day_name, 1 ordby UNION ALL
SELECT 'Monday' day_name, 2 ordby UNION ALL
SELECT 'Tuesday' day_name, 3 ordby UNION ALL
SELECT 'Wednesday' day_name, 4 ordby UNION ALL
SELECT 'Thursday' day_name, 5 ordby UNION ALL
SELECT 'Friday' day_name, 6 ordby UNION ALL
SELECT 'Saturday' day_name, 7 ordby
) a
LEFT JOIN
(
SELECT DAYNAME(timestamp) day_name,
COUNT(*) totalCount
FROM `emp_info`
WHERE DATE(timestamp ) > DATE_SUB(CURDATE( ) , INTERVAL 1 WEEK )
GROUP BY DAYNAME(timestamp)
) b ON a.day_name = b.day_name
ORDER BY a.ordby