CASE语句WHERE子句中！=条件

Question

我想弄清楚如何在where子句中使用case语句（with！=），这里是我想要做的事情的一个想法：

SELECT * 
FROM Table1 JOIN Table2 JOIN Table3 
WHERE 
    CASE @fruit 
    WHEN 'Apples' THEN (What would go here to return only data related to apples in Table1?) 
    WHEN 'Citrus' THEN (What would go here to return data related to either oranges or lemons in Table2?) 
    WHEN 'Other' THEN (return all data not related to apples, oranges, or lemons from all 3 tables) (!=) 
    END 

我在where子句中看到了case语句的几个例子，但没有一个带有！=的条件。有任何想法吗？

Answer 1

如果我理解你的问题，你想评估其他布尔表达式除了平等。该CASE语句有两种形式，即你想要一个（总是找平等）和这个其他形式：

CASE 
    WHEN <boolean expression> THEN <result expression> 
    WHEN <boolean expression> THEN <result expression> 
    ELSE <else expression> 
END 

Answer 2

简单AND/OR组合会做：

SELECT * 
FROM Table 
WHERE 
    (@fruit != 'Other' AND Fruit = @fruit) OR 
    (@fruit = 'Other' AND Fruit NOT IN('Apples', 'Oranges') 

Answer 3

只是使用ELSE的一切

SELECT * 
FROM Table 
WHERE 
    CASE @fruit 
    WHEN 'Apples' THEN (What would go here to return only data related to apples?) 
    WHEN 'Oranges' THEN (What would go here to return only data related to oranges?) 
    ELSE (return all data not related to apples or oranges) (!=) 
    END 

或者您也可以使用参数的情况里面，像这样

SELECT * 
FROM Table 
WHERE 
    CASE 
    WHEN @fruit = 'Apples' THEN (What would go here to return only data related to apples?) 
    WHEN @fruit = 'Oranges' THEN (What would go here to return only data related to oranges?) 
    WHEN @fruit <> 'Apples' AND @fruit <> 'Oranges' THEN (return all data not related to apples or oranges) (!=) 
    END