有条件的交叉连接

Question

我正在使用交叉联接来重复从数据库输出的行。

我想要一个过滤器，以便仅重复某些值

这就是我到目前为止

SELECT EmployeeID, EmployeeForeName From Employee 
CROSS JOIN
(SELECT TOP 2 Number FROM Numbers) Numbers
WHERE EmployeeID in (20,30)

这输出为

EmployeeID  EmployeeForeName
20          Jamie
30          Karl
20          Jamie
30          Karl

我将如何执行，但仅在EmployeeID = 20的情况下重复； 结果如下

EmployeeID  EmployeeForeName
20          Jamie
30          Karl
20          Jamie

谢谢！

Answer 1

尝试这个：

SELECT e.EmployeeID, e.EmployeeForeName 
FROM Employee AS e
CROSS APPLY
   (SELECT t.n
    FROM (VALUES (1), (2)) AS t(n)
    WHERE (t.n = 1) OR (e.EmployeeID = 20)) AS x
WHERE e.EmployeeID in (20,30)

Answer 2

您似乎不需要两个值的cross join 。

SELECT EmployeeID, EmployeeForeName
FROM Employee CROSS JOIN
     (SELECT TOP 2 Number FROM Numbers) Numbers
WHERE EmployeeID IN (20)
UNION ALL
SELECT EmployeeID, EmployeeForeName
FROM Employee
WHERE EmployeeID IN (30);

Answer 3

我了解您只希望复制EmployeeId 20，而不要复制30，我不知道Numbers表中的内容，我会在下面进行操作

DECLARE @TBL AS TABLE 
(
    EmployeeID INT, EmployeeForeName VARCHAR(100)
)

INSERT INTO @TBL
SELECT 20 EmployeeID,'Jamie' EmployeeForeName
UNION ALL
SELECT 20,'Jamie'
UNION ALL
SELECT 30,'Karl'
UNION ALL
SELECT 30,'Karl'

select * from @TBL where EmployeeID =20
union all
select distinct * from @TBL where EmployeeID =30

Answer 4

尝试这个

SELECT EmployeeID, EmployeeForeName From Employee 
CROSS JOIN
(SELECT TOP 2 Number FROM Numbers) Numbers
WHERE EmployeeID =20
union all
SELECT EmployeeID, EmployeeForeName
FROM Employee
WHERE EmployeeID =30

Answer 5

这样的事情应该可以解决问题。

SELECT EmployeeID, EmployeeForeName From Employee 
CROSS JOIN
(SELECT TOP 2 Number FROM Numbers) Numbers
WHERE EmployeeID = 20
UNION ALL 
SELECT EmployeeID, EmployeeForeName From Employee 
WHERE EmployeeID  = 30