如何在MS-Access中计算三个不同的不同值并在ID上分组？

Question

所以我知道MS-Access不允许SELECT COUNT(DISTINCT....) FROM ... ，但是我正在尝试找到一种更可行的替代常规标准的方法。

SELECT COUNT(*) FROM (SELECT DISTINCT Name FROM table1)

我的问题是我试图做三个单独的Count函数并将它们按ID分组。 如果使用上述方法，它将为我提供整个表的总唯一值计数，而不是仅给ID值的总计数。 我试着做

(SELECT COUNT(*) FROM (SELECT DISTINCT Name FROM table1 as T2
WHERE T2.ColumnA = T1.ColumnA)) As MyVal
FROM table1 as T1

但是它告诉我我需要为T1.ColumnA指定一个值。

我要完成的SQL查询是这样的：

SELECT ID
COUNT(DISTINCT ColumnA) as CA,
COUNT(DISTINCT ColumnB) as CB,
COUNT(DISTINCT ColumnC) as CC
FROM table1
GROUP BY ID

有任何想法吗？

Answer 1

您可以使用子查询。 假设您有一个表，每个ID都出现一次：

select (select count(*)
        from (select columnA
              from table1 t1
              where t1.id = t.id
              group by columnA
             ) as a
       ) as num_a,
       (select count(*)
        from (select columnB
              from table1 t1
              where t1.id = t.id
              group by columnB
             ) as b
       ) as num_b,
       (select count(*)
        from (select columnC
              from table1 t1
              where t1.id = t.id
              group by columnC
             ) as c
       ) as num_c
from <table with ids> as t;

我不确定您是否认为这是“可行的”。

编辑：

这使其更加复杂。 。 。 这表明MS Access不支持超过一个级别的关联子句（您是否考虑切换到另一个数据库？）。

无论如何，蛮力方式：

select a.id, a.numA, b.numB, c.numC
from ((select id, count(*) as numA
       from (select id, columnA
             from table1 t1
             group by id, columnA
            ) as a
      ) as a inner join
      (select id, count(*) as numB
       from (select id, columnB
             from table1 t1
             group by id, columnB
            ) as b
      ) as b
      on a.id = b.id
     ) inner join
     (select id, count(*) as numC
      from (select id, columnC
            from table1 t1
            group by id, columnC
           ) as c
     ) c
     on c.id = a.id;