如何在MySQL中使用一个命令对两个表中的行进行计数

Question

我想从不同的表中计数2个表，即时通讯选择date然后将其分组。

这是我尝试的

SELECT 
(SELECT date(date), COUNT(sh_sh) FROM sh_url GROUP BY date(date)) AS URLs, 
(SELECT date(date), COUNT(ip) FROM tracking GROUP BY date(date)) AS IP 
FROM dual

但我得到错误

1241-操作数应包含1列

用一个命令就能做到吗？

输出应该是这样的

date(url)    count(sh_sh)    date(ip)    count(ip)
---------    ------------    ----------  ----------
2018-04-25   123             2018-04-25  123123
2018-04-26   456             2018-04-26  321
2018-04-27   789             2018-04-27  3125

Answer 1

我用两个子查询的连接来表达您的问题：

SELECT
    t1.date,
    t1.url_cnt,
    COALESCE(t2.ip_cnt, 0) AS ip_cnt
FROM
(
    SELECT date, COUNT(*) url_cnt
    FROM sh_url
    GROUP BY date
) t1
LEFT JOIN
(
    SELECT date, COUNT(*) ip_cnt
    FROM tracking
    GROUP BY date
) t2
    ON t1.date = t2.date;

Answer 2

当使用子查询作为值时，它只能返回一行和一列。 您需要使用JOIN ：

SELECT urls.date, urls.count AS sh_count, ip.count AS ip_count
FROM (SELECT date(date) AS date, COUNT(*) AS count FROM sh_url GROUP BY date(date)) AS urls
JOIN (SELECT date(date) AS date, COUNT(*) AS count FROM tracking GROUP BY date(date)) AS ip
ON urls.date = ip.date