如何在 MS Access 中向 SQL 查询添加自定义行？

Question

我尝试使用 UNION 但我曾经收到此消息：

查询输入必须至少包含一个表或查询

我尝试的查询是：

SELECT NULL AS ID, NULL AS Item
  UNION 
    SELECT Items.ID AS ID, Items.Item as Item
    FROM Items 
    INNER JOIN People 
    ON Items.PID=People.PID
    WHERE People.Name='John';

两个 select 语句都可以独立运行。

Answer 1

使用Dual 表

SELECT NULL AS ID, NULL AS Item
FROM dual
UNION ALL
SELECT i.ID AS ID, i.Item AS Item
FROM Items i
INNER JOIN People p ON i.PID = p.PID
WHERE p.Name = 'John';

Answer 2

在 MS Access 中，您将需要使用 kludge。这可能有效：

SELECT TOP 1 NULL AS ID, NULL AS Item
FROM (SELECT TOP 1 *
      FROM ITEMS
      ORDER BY ID
     ) as i
UNION ALL
SELECT Items.ID AS ID, Items.Item as Item
FROM Items INNER JOIN
     People
     ON Items.PID = People.PID
WHERE People.Name = 'John';

子查询的唯一目的是获取包含一行的表。请记住，MS Access 中的TOP 1 如果存在平局，则可以返回多行。

Answer 3

您需要指定要从哪个表中获取数据。试试这个：

SELECT NULL AS ID, NULL AS Item
FROM Items INNER JOIN People ON Items.PID=People.PID
UNION 
SELECT Items.ID AS ID, Items.Item as Item
FROM Items INNER JOIN People ON Items.PID=People.PID
WHERE People.Name='John';

Answer 4

也许如果联合查询顺序更改为从形成的查询开始，然后是空查询：

SELECT Items.ID AS ID, Items.Item as Item
FROM Items 
INNER JOIN People 
ON Items.PID=People.PID
WHERE People.Name='John'

union 

SELECT NULL AS ID, NULL AS Item