两个表a,b 输出a,b关联的当月每天的数据的行数,当天没有数据为0
时间: 2024-02-21 16:01:14 浏览: 20
可以使用以下 SQL 查询语句实现:
```
SELECT DATE_FORMAT(a.date, '%Y-%m-%d') AS day, COUNT(b.*) AS count
FROM a
LEFT JOIN b ON DATE_FORMAT(a.date, '%Y-%m-%d') = DATE_FORMAT(b.date, '%Y-%m-%d')
GROUP BY day;
```
上面的查询语句中,我们首先使用 `LEFT JOIN` 将表 `a` 和表 `b` 连接起来,然后使用 `DATE_FORMAT` 函数将日期格式化成 `%Y-%m-%d` 的形式,这样就可以按天进行分组。最后使用 `COUNT` 函数统计每天 `b` 表的行数,如果当天没有数据,就会返回 0。
注意:以上 SQL 语句仅供参考,具体实现需要根据实际的数据表结构进行调整。
相关问题
输出当月每天的数据,当天没有数据为0 mysql
假设你有一个名为 `table` 的表,其中包含一个 `date` 字段表示日期,以及其他数据字段,你可以使用以下 SQL 语句输出当月每天的数据,当天没有数据为 0:
```
SELECT DATE_FORMAT(date, '%Y-%m-%d') AS date, COALESCE(SUM(data), 0) AS data
FROM (
SELECT DATE_FORMAT(date, '%Y-%m-%d') AS date, data
FROM table
WHERE date BETWEEN DATE_FORMAT(NOW(), '%Y-%m-01') AND LAST_DAY(NOW())
) AS t
RIGHT JOIN (
SELECT DATE_FORMAT(date, '%Y-%m-%d') AS date
FROM (
SELECT DATE_FORMAT(DATE_ADD(DATE_FORMAT(NOW(), '%Y-%m-01'), INTERVAL (tens+units) DAY), '%Y-%m-%d') AS date
FROM (
SELECT 0 AS tens UNION SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7 UNION SELECT 8 UNION SELECT 9
) AS t1
CROSS JOIN (
SELECT 0 AS units UNION SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7 UNION SELECT 8 UNION SELECT 9
) AS t2
WHERE DATE_ADD(DATE_FORMAT(NOW(), '%Y-%m-01'), INTERVAL (tens+units) DAY) <= LAST_DAY(NOW())
) AS days
) AS days
ON t.date = days.date
GROUP BY days.date
ORDER BY days.date;
```
该 SQL 语句使用了一个右连接(RIGHT JOIN)来保证输出当月所有天数的数据,即使当天没有数据也要输出 0。其中,子查询 `days` 生成了当前月份的所有日期,子查询 `t` 获取了当前月份内的所有数据,最后使用 `GROUP BY` 和 `SUM` 函数对数据进行聚合,生成当月每天的数据。
mysql中统计当月每天的数据数量,没有数据,那天的数量赋值为0
可以使用以下SQL语句来获取当月每天的数据数量,并将没有数据的日期数量赋值为0:
```
SELECT DATE(date_column) AS date, COUNT(*) AS count
FROM (
SELECT DATE_FORMAT(CURRENT_DATE(), '%Y-%m-%d') - INTERVAL (a.a + (10 * b.a) + (100 * c.a)) DAY AS date
FROM (
SELECT 0 AS a UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
) AS a
CROSS JOIN (
SELECT 0 AS a UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
) AS b
CROSS JOIN (
SELECT 0 AS a UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
) AS c
) AS dates
LEFT JOIN table ON DATE(date_column) = dates.date
WHERE MONTH(dates.date) = MONTH(CURRENT_DATE())
GROUP BY dates.date
ORDER BY dates.date;
```
其中,`date_column`是包含日期的列名,`table`是表名。这条SQL语句会把当月的每一天的数量分别统计出来,并将没有数据的日期数量赋值为0。