条件选择？

Question

我有以下SQL代码：

SELECT eml AS "Email Address" 
FROM emailtbl 
WHERE DEPT LIKE 'E%' 

我的问题是，如果部门“F”开头我必须选择传真，而不是EML。我应该怎么做，如果部门与“E”，然后选择传真开始选择EML如果部门在“F”

由于开始

Answer 1

一种选择是使用UNION ALL声明

SELECT eml AS "Entity" 
FROM emailtbl 
WHERE DEPT LIKE 'E%' 
UNION ALL 
SELECT fax AS "Entity" 
FROM emailtbl 
WHERE DEPT LIKE 'F%' 

另一种是使用CASE声明

SELECT CASE WHEN Dept LIKE 'E%' THEN eml ELSE fax END AS "Entity" 
FROM emailtbl 
WHERE DEPT LIKE 'E%' OR DEPT LIKE 'F%' 

Answer 2

如何

样？

IF (SUBSTRING(@useLike,1,1) = 'E') 
BEGIN 
    SELECT eml AS "Email Address" 
    FROM emailtbl 
    WHERE DEPT LIKE @useLike 

END 
ELSE 
BEGIN 
    SELECT fax AS "Email Address" 
    FROM emailtbl 
    WHERE DEPT LIKE @useLike 
END