MS Access SQL-删除没有重复/重复的重复项

Question

我在MS Access中工作，需要从[ref]字段中删除重复的值，而无需使用不同的（无法在Access中的特定字段上使用）和分组依据（因为我想按[type]分组）。

我尝试使用其他子查询对[ref]字段进行重复数据删除，但是无法使其正常工作。下面的代码有效，但是在[ref]字段中包含重复的值。

SELECT
    switch(LEFT(t1.[type],1)='C',"Covers",LEFT(t1.[type],1)='P',"PIP") AS type
  , COUNT(t1.[ref])
  , COUNT(t2.[posted]) AS Total_posted
  , format(COUNT(t2.[posted]) / COUNT(t1.[ref]),"0.00%") AS Percentage_posted
FROM
    Some_Table AS t1
    LEFT JOIN
        (
            SELECT
                t2.[ID]
              , t2.[posted]
            FROM
                Some_Table AS t2
            WHERE
                t2.[posted] NOT LIKE ('NA')
        )
        AS t2
    ON
        t1.[ID] = t2.[ID]
GROUP BY
    LEFT(t1.[type],1)

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编辑：以下示例场景

t1。[ref]

• 1
• 1
• 1
• 2
• 3
• 4
• 5

当前代码将返回t1的COUNT。[ref]为7，但是我希望输出返回5的计数。

进一步编辑：现在，如下所示编写代码，但是t3。[ref]仍未提供不同的值。知道我在哪里错了吗？

    SELECT Switch(Left(t1.[type],1)='C',"Covers",Left(t1.[type],1)='P',"PIP") AS type, Count(t3.[ref]) AS CountOfref, Count(t2.[posted]) AS Total_posted, Format(Count(t2.[posted])/Count(t1.[ref]),"Percent") AS Percentage_posted
FROM (additional_data_fields AS t1 LEFT JOIN (Select t2.[ID],t2.[posted] from additional_data_fields as t2 where t2.[posted] not like ('NA'))  AS t2 ON t1.[ID] = t2.[ID]) LEFT JOIN (select distinct t3.[ref] from additional_data_fields as t3)  AS t3 ON t1.[ref] = t3.[ref]
GROUP BY Left(t1.[type],1)