mysql - 计算 2 个表的相等字段，并与第 3 个表进行内部连接

Question

我有3张 table

Table cases: docket is pk 
| docket |   dt_file  |
-----------------------
|AA-0322 | 01-22-2015 |
|AA-0431 | 03-21-2014 |


Table parties:
|  id  |  docket  |  name  |
----------------------------
|   1  |  AA-0322 |  Bob   |
|   2  |  AA-0322 |  John  |


Table motions:
|  id  |  docket  |  motion |
-----------------------------
|  1   | AA-0322  |  Summons|
|  2   | AA-0322  |  Guilty |

我想计算具有相同摘要的政党和动议中的字段数，然后用 table.cases 和 dt_file 制作一个表格

例子:

| docket | party_count | motion_count| dt_file |
 -----------------------------------------------
  AA-0322|       2     |        2    | 02-22-2015|

我也想通过dt_file过滤，所以添加一个WHERE语句ex:

WHERE YEAR(dt_file) = '2015'

到目前为止，我已经想到了这个，但是我没有成功地将 table.cases 与 dt_file 正确地连接起来。

SELECT p.docket, p.party_count, m.motion_count
FROM
    (SELECT docket, COUNT(docket) AS party_count
     FROM parties
     GROUP BY docket) AS p
INNER JOIN
    (SELECT docket, COUNT(docket) AS motion_count
     FROM motions
     GROUP BY docket) AS m
ON p.docket = m.docket

Answer 1

您的查询似乎是正确的。您只需要将 cases 添加到 from 子句:

SELECT c.docket, p.party_count, m.motion_count, c.dt_file
FROM cases c JOIN
     (SELECT docket, COUNT(docket) AS party_count
      FROM parties
      GROUP BY docket
     ) p
     ON c.docket = p.docket INNER JOIN
     (SELECT docket, COUNT(docket) AS motion_count
      FROM motions
      GROUP BY docket
     ) m
     ON c.docket = m.docket;

如果您想要所有的摘要，即使是那些没有议案或派对的摘要，那么使用 LEFT JOIN。