Question

我想做一个类似于SQL的语句，我无法理解它。

如果我的 TABLE_A 看起来像这样：

[dbo].[TABLE_A](
    [EmpID] [INT],
    [FName] [varchar](50) NULL,
    [LName] [varchar](50) NULL
)

...我的 TABLE_B 如下所示：

[dbo].[TABLE_B](
    [EmployeeActivity] [varchar](50) NULL,
    [EmpID] [INT]
)

有人可以帮我写一个查询来做这样的事情：

FOR EACH DISTINCT [EmployeeActivity] RETURN 
  [TABLE_B].[EmployeeActivity],
  [TABLE_A].[FName], 
  [TABLE_A].[LName], 
  [TABLE_A].[EmpID],
  CASE
    WHEN ([TABLE_B].[EmployeeActivity] IS NULL) THEN ('NO')
  ELSE 'YES'
  END

结果应该如下：

FireDrill12, Bill, Jones, 342,YES
FireDrill13, Bill, Jones, 342,NO
FireDrill14, Bill, Jones, 342,YES
FireDrill12, Smith, Sue, 253,NO
FireDrill13, Smith, Sue, 253,NO
FireDrill14, Smith, Sue, 253,YES

我无法理解这一点。

感谢您的帮助，

-Allen

Answer 1

SELECT DISTINCT 
       [TABLE_A].[EmpID], [TABLE_A].[FName], [TABLE_A].[LName] 
     , CASE
          WHEN [TABLE_B].[EmployeeActivity] IS NULL THEN 'No'
          ELSE 'Yes'
       END AS [EmployeeActivity]
  FROM [TABLE_A]
  LEFT JOIN [TABLE_B] 
    ON [TABLE_B].[EmpID] = [TABLE_A].[EmpID]

Answer 2

SQL无论如何都是一种基于集合的语言，所以它已经为每个＆＃34;做了事情，所以理论上你可以做一个CROSS JOIN来获得每个组合，用相关的查询来做你的检查，所以可能是这样的：

SELECT DISTINCT
            b.EmployeeActivity,
            a.FName,
            a.LName,
            a.EmpId,
            CASE 
                WHEN EXISTS (SELECT 1 FROM [TABLE_B] c WHERE c.[EmployeeActivity] = b.EmployeeActivity AND c.EmpId = a.EmpId) THEN 'YES' 
                ELSE 'NO' 
            END

FROM        Table_b AS b

CROSS JOIN  Table_a AS a
    ON      a.EmpId = b.EmpId

Answer 3

使用inner加入的另一个版本，但使用left加入的更正确的版本如@Blam

所示

SELECT 
    A.*, 
    CASE
        WHEN B.EmployeeActivity IS NULL THEN 'No'
        ELSE 'Yes'
    END
FROM
[dbo].[TABLE_A] A
INNER JOIN [dbo].[TABLE_B] B ON (A.EmpID = B.EmpID)
UNION
SELECT 
    A.*, 
    'No'
FROM
[dbo].[TABLE_A] A
WHERE 
A.EmpID NOT IN (SELECT B.EmpID FROM [dbo].[TABLE_B] B)

TSQL - For Each like Statement

3 个答案: