與條件交叉連接

Question

我正在使用交叉連接來複制從我的數據庫輸出的行。

我想一個過濾器，以便只有特定的值複製

這是我迄今爲止

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

此輸出作爲

EmployeeID EmployeeForeName 
20   Jamie 
30   Karl 
20   Jamie 
30   Karl 

我怎麼會做這個，但僅在EmployeeID = 20時重複;導致以下內容

EmployeeID EmployeeForeName 
20   Jamie 
30   Karl 
20   Jamie 

謝謝！

Answer 1

您似乎不希望兩個值都有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

試試這個

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

像這樣的東西應該做的伎倆;

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

試試這個：

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)