MS Access 查询 SQL 联合 Select 返回 -1

Question

我有一个带有 SQL Union Select 的 MS Access 查询，它在我的报告中返回 -1。 我假设 -1 是因为查询返回 null 值，但我无法弄清楚如何使用 IFF() 语句停止在报告中显示 -1。 这是 SQL 查询：

SELECT [Employees].[Last Name] & ", " & [First Name] AS EmployeeName, Employees.[Active Employee], Employees.[Active Employee], Employees.[Active Employee]
FROM Employees
WHERE (((Employees.[Active Employee])=True))
ORDER BY [Employees].[Last Name] & ", " & [First Name];

UNION SELECT [Employees].[Last Name] & ", " & [First Name] AS EmployeeName, TypeOfAbsence.TypeOfAbsence, [Vacation Calendar].[Date Used], [Vacation Calendar].Time
FROM TypeOfAbsence INNER JOIN (Employees INNER JOIN [Vacation Calendar] ON Employees.ID = [Vacation Calendar].EmployeeID) ON TypeOfAbsence.ID = [Vacation Calendar].TypeID
WHERE ((([Vacation Calendar].[Date Used])<[Forms]![Week Ending Report Form]![End_Date] And ([Vacation Calendar].[Date Used])>[Forms]![Week Ending Report Form]![Start_Date]));

Answer 1

考虑使用 Null 作为 UNION 的字段占位符。 这将从重复的 [Active Employee] 字段中消除 -1 值。 删除嵌入的分号，因为这将导致 UNION 失败。 ORDER BY 子句可能没用，因为排序应该由报表管理，如果设置了报表排序和分组，查询顺序肯定会被忽略。 第一个 SELECT 行定义字段数据类型和名称。 不需要在后续的 SELECT 行中重复别名字段名称。

SELECT [Last Name] & ", " & [First Name] AS EmployeeName, Null AS TOA, Null AS DU, Null AS TU
FROM Employees
WHERE (((Employees.[Active Employee])=True))

UNION SELECT [Last Name] & ", " & [First Name], TypeOfAbsence, [Date Used], [Time] 
FROM TypeOfAbsence 
INNER JOIN (Employees INNER JOIN [Vacation Calendar] 
ON Employees.ID = [Vacation Calendar].EmployeeID) 
ON TypeOfAbsence.ID = [Vacation Calendar].TypeID
WHERE ((([Vacation Calendar].[Date Used])<[Forms]![Week Ending Report Form]![End_Date] And ([Vacation Calendar].[Date Used])>[Forms]![Week Ending Report Form]![Start_Date]));

还要考虑这个过滤条件：
WHERE [Date Used] BETWEEN [Forms]![Week Ending Report Form]![Start_Date] AND [Forms]![Week Ending Report Form]![End_Date]