与条件交叉连接

Question

我正在使用交叉连接来复制从我的数据库输出的行。

我想一个过滤器，以便只有特定的值复制

这是我迄今为止

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

此输出作为

EmployeeID EmployeeForeName 
20   Jamie 
30   Karl 
20   Jamie 
30   Karl 

我怎么会做这个，但仅在EmployeeID = 20时重复;导致以下内容

EmployeeID EmployeeForeName 
20   Jamie 
30   Karl 
20   Jamie 

谢谢！

Answer 1

您似乎不希望两个值都有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 2

试试这个

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 3

像这样的东西应该做的伎俩;

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 4

试试这个：

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)