Question

我有以下SQL语句，即使我有300名员工，它也只返回2条记录。有谁看到我可能做错了什么？

SELECT     Employees.[Employee ID], 
Employees.Employee, 
Employees.[First Name], 
Employees.[Middle Name], 
Employees.[Last Name], 
Employees.Position,
[Work].[Work ID]
FROM  Employees LEFT JOIN
[Work] ON Employees.[Employee ID] = [Work].[Employee ID]
WHERE [Work].[Work Date] = '06-13-2012'

Answer 1

在外表上使用外连接过滤器时必须在ON子句中应用，否则有效地获得内连接：

SELECT     
    Employees.[Employee ID], 
    Employees.Employee, 
    Employees.[First Name], 
    Employees.[Middle Name], 
    Employees.[Last Name], 
    Employees.Position,
    [Work].[Work ID]
FROM  Employees 
LEFT JOIN [Work] 
  ON Employees.[Employee ID] = [Work].[Employee ID]
 AND [Work].[Work Date] = '06-13-2012'

Answer 2

如果您想要所有员工，也许您正在寻找以下内容：

SELECT     Employees.[Employee ID],  ...
FROM  Employees LEFT JOIN 
[Work] ON Employees.[Employee ID] = [Work].[Employee ID] 
AND [Work].[Work Date] = '20120613'

另请注意，您应使用明确的日期格式，例如YYYYMMDD

Answer 3

您是否在Where子句中检查了日期？

尝试转换为日期时间或检查您是否在[工作]。[工作日期]列数据中定义了小时/分钟/秒。

尝试删除联接以查看问题所在：

SELECT [Work].[Employee ID], [Work].[Work ID]
FROM [Work]
WHERE [Work].[Work Date] = '06-13-2012'

您有多少条记录？所有员工ID是否与Employees表中的ID匹配？

如果您需要所有员工而不是您应该进行LEFT OUTER JOIN：

SELECT     Employees.[Employee ID], 
Employees.Employee, 
Employees.[First Name], 
Employees.[Middle Name], 
Employees.[Last Name], 
Employees.Position,
[Work].[Work ID]
FROM  Employees LEFT OUTER JOIN
[Work] ON Employees.[Employee ID] = [Work].[Employee ID]
AND [Work].[Work Date] = '06-13-2012'

这是你想要的吗？

Answer 4

还尝试查看[工作日期]栏 - 如果它还有时间部分（日期时间数据类型），那么你应该考虑到这一点：

SELECT     
    Employees.[Employee ID], 
    Employees.Employee, 
    Employees.[First Name], 
    Employees.[Middle Name], 
    Employees.[Last Name], 
    Employees.Position,
    [Work].[Work ID]
FROM  Employees 
LEFT JOIN [Work] 
  ON Employees.[Employee ID] = [Work].[Employee ID]
WHERE Convert(Char(10), [Work].[Work Date], 120) = '2012-06-13' -- can find better way

使用LEFT JOIN时没有收到预期的结果？

4 个答案: