mysql - SQL Join 来自另一个表的数据计数

Question

我有数据库

来自标签用户列表

NO NAMA DATE
1  THIS 2019-01-17 18:40:45
2  IS   2019-01-17 18:40:45
3  NAME 2019-02-17 18:40:45

来自表格用户文本

ID TEXT CREATE
1  THIS 2019-01-18 18:40:45
2  IS   2019-02-21 18:40:45
3  TEXT 2019-03-19 18:40:45

如何使用 sql 查询返回这样的结果

Month Name Text
Jan   2    1
Feb   1    1
Mar   0    1

我已经试过了

SELECT MONTHNAME(userlist.date) as Month, COUNT(userlist.no) as name, COUNT(usertext.id) as text FROM userlist, usertext WHERE MONTH(userlist.date) < 12 AND YEAR(userlist.date) = YEAR(CURRENT_TIMESTAMP) GROUP BY MONTHNAME(date)

然后像这样返回

Month Name Text
Jan   1    1
Feb   1    1
Mar   1    1

Answer 1

联合，然后聚合。

SELECT Month, SUM(usr) as Name, SUM(txt) as Text
FROM
(
    SELECT MONTH(t.date) AS monthnum, MONTHNAME(t.date) AS Month, 1 AS usr, 0 AS txt
    FROM userlist t
    WHERE YEAR(t.date) = YEAR(CURRENT_TIMESTAMP) 
      AND MONTH(t.date) < 12 

    UNION ALL

    SELECT MONTH(t.create) AS monthnum, MONTHNAME(t.create) AS Month, 0 AS usr, 1 AS txt
    FROM usertext t
    WHERE YEAR(t.create) = YEAR(CURRENT_TIMESTAMP) 
      AND MONTH(t.create) < 12
) q
GROUP BY monthnum, Month
ORDER BY monthnum 

下面是一小段生成 12 个月的 sql。它可以是内部查询中的额外 UNION ALL，以填补缺失月份的空白。

select n as monthnum, monthname(100*n+1) as month, 0 as usr, 0 as txt
from (
    select 1 as n 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 union all select 10 union all select 11 union all select 12
) q