sql - COUNT DISTINCT WITH CONDITION 和 GROUP BY

Question

我想根据特定条件计算列中不同项目的数量。例如，如果表格是这样的:

ID | name   |    date    | status
---+--------+------------+--------
1  | Andrew | 2020-04-12 | true
2  | John   | 2020-03-22 | null
3  | Mary   | 2020-04-13 | null
4  | John   | 2020-05-27 | false
5  | Mary   | 2020-02-08 | true
6  | Andrew | 2020-02-08 | null

如果我想将最后日期的状态不为空的不同名称的数量统计为“名称计数”，并按状态对它们进行分组，我应该怎么做？

结果应该是:

status | name_count
-------+-----------
true   | 1            ---> Only counts Andrew (ID 1 has the last date)
false  | 1            ---> Only counts John (ID 4 has the last date)  

Answer 1

你可以试试下面的查询

SELECT COUNT(DISTINCT Name), Status 
  FROM Table
  WHERE Status IS NOT NULL
 GROUP BY Status;