使用 SQL 查询将返回的记录限制为唯一

Question

我正在使用 Microsoft Access 来设计一个查询（我最终将在我的 MFC 应用程序中提取并使用它。到目前为止，我有这个：

SQL 视图是：

SELECT [Congregation Speaker Talks].talkno, [Congregation Speaker Talks].congregation
FROM [Congregation Speaker Talks]
WHERE ((([Congregation Speaker Talks].congregation)<>'Keynsham'))
ORDER BY [Congregation Speaker Talks].talkno;

目前的结果是：

所以它正在工作，因为没有列出值为 Keynsham 的记录。但正如你所看到的，有来自不同会众的多位演讲者进行了第 1 次演讲。我只希望这个数字出现一次。我尝试使用DISTINCT，但它不起作用。

更新

这有点帮助：

SQL "select where not in subquery" returns no results

我向您展示了我所做的，但我想避免将查询实际添加到表中。

第 1 步 我创建了一个查询并将其保存为KeynshamTalks：

SELECT [Public Talk Titles].[Talk Number]
FROM [Public Talk Titles] INNER JOIN [Congregation Speaker Talks] ON [Public Talk Titles].[Talk Number] = [Congregation Speaker Talks].talkno
WHERE ((([Congregation Speaker Talks].congregation)="Keynsham"))
ORDER BY [Public Talk Titles].[Talk Number], [Congregation Speaker Talks].congregation;

此查询返回所有会众演讲者谈话号码的列表，其中会众IS 设置为 Keynsham。

第 2 步 接下来，我在 Public Talk Titles 表上创建了一个新查询。该表每个通话号码只有一次。我使用KeynshamTalks查询的结果作为子查询：

SELECT *
FROM [Public Talk Titles]
WHERE ((([Public Talk Titles].[Talk Number]) Not In (SELECT [Talk Number]
FROM
[KeynshamTalks]
)))
ORDER BY [Public Talk Titles].[Talk Number];

这行得通。结果正是我想看到的。但是我怎样才能将第一个查询直接移动到第二个查询中，使其成为一个查询呢？

Answer 1

您应该使用NOT EXISTS 而不是NOT IN 编写查询：

SELECT ptt.*
FROM [Public Talk Titles] as ptt
WHERE NOT EXISTS (SELECT 1
                  FROM [Congregation Speaker Talks] as cst
                  WHERE ptt.[Talk Number] = cst.talkno AND
                        cst.congregation = "Keynsham"
                 )
ORDER BY ptt.[Talk Number];

注意表别名（并去掉不需要的括号）如何使查询更易于编写和阅读。

如果您只想要谈话的一个子集，那么在外部查询中添加一个WHERE 子句。

Answer 2

这就是我想要的：

SELECT *
FROM [Public Talk Titles]
WHERE ((([Public Talk Titles].[Talk Number]) Not In (
SELECT [Public Talk Titles].[Talk Number]
FROM [Public Talk Titles] INNER JOIN [Congregation Speaker Talks] ON [Public Talk Titles].[Talk Number] = [Congregation Speaker Talks].talkno
WHERE ((([Congregation Speaker Talks].congregation)="Keynsham"))
)))
ORDER BY [Public Talk Titles].[Talk Number];