WHERE子句中的CASE语句，带有！= condition

I'm trying to figure out how to use a case statement in a where clause (with !=), here is an idea of what I am trying to do:

我试图弄清楚如何在where子句中使用case语句（使用！=），这里是我想要做的事情的想法：

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

I've seen a few examples of a case statement in a where clause, but not one with a != condition. Any ideas?

我在where子句中看到了一些case语句的例子，但没有一个带有！=条件的例子。有任何想法吗？

3 个解决方案

#1

A simple AND/OR combination will do:

一个简单的AND / OR组合将：

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

#2

If I understood your question, you want to evaluate other boolean expression besides equality. The CASE statement has two forms, the one that you're trying (always look for equality) and this other form:

如果我理解你的问题，你想要评估除了相等之外的其他布尔表达式。 CASE语句有两种形式，一种是你正在尝试的（总是寻找相等）和另一种形式：

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

#3

just use ELSE for everything else

只需将ELSE用于其他一切

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

OR you can use the parameter inside the case, like this

或者您可以使用案例中的参数，就像这样

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

#1