如何修改此t-sql查询以返回不同列名的最大值？

Question

我有以下查询：

SELECT 
     [Rate], 
     [RateMon], 
     [RateTue], 
     [RateWed], 
     [RateThu], 
     [RateFri], 
     [RateSat], 
     [RateSun] 
    FROM 
     [Room] 
    WHERE 
     Id=@Id 

，而不是返回所有列的，我只是想回到Rate和RateMon，RateTue，RateWed，RateThu，RateFri，RateSat和RateSun之间的最大价值，但我由于列名是不同的，所以我很难过。

一个例子结果恢复现在是：

100，400，400，400，400，600，600，600

其中100是速度和其他值对应于周一 - 周日，但我想在这种情况下返回100和600。

Answer 1

SELECT [Rate], 
     (SELECT MAX(T.[Rate]) 
     FROM (VALUES([RateMon]), 
        ([RateTue]), 
        ([RateWed]), 
        ([RateThu]), 
        ([RateFri]), 
        ([RateSat]), 
        ([RateSun])) AS T([Rate]) 
     ) AS MaxRate 
FROM [Room] 
WHERE Id=@Id 

Answer 2

您可以使用一些详细的喜欢：

SELECT Rate, 
    CASE 
    WHEN RateMon>=RateTue AND RateMon>=RateWed AND RateMon>=RateThu AND 
     RateMon>=RateFri AND RAteMon>=RateSat AND RateMon>=RateSun THEN RateMon 
    WHEN RateTue>=RateMon AND RateTue>=RateWed AND RateTue>=RateThu AND 
     RateTue>=RateFri AND RateTue>=RateSat AND RateTue>=RateSun THEN RateTue 
    WHEN RateWed>=RateMon AND RateWed>=RateTue AND RateWed>=RateThu AND 
     RateWed>=RateFri AND RateWed>=RateSat AND RateWed>=RateSun THEN RateWed 
    WHEN RateThu>=RateMon AND RateThu>=RateTue AND RateThu>=RateWed AND 
     RateThu>=RateFri AND RateThu>=RateSat AND RateThu>=RateSun THEN RateThu 
    WHEN RateFri>=RateMon AND RateFri>=RateTue AND RateFri>=RateWed AND 
     RateFri>=RateThu AND RateFri>=RateSat AND RateFri>=RateSun THEN RateFri 
    WHEN RateSat>=RateMon AND RateSat>=RateTue AND RateSat>=RateWed AND 
     RateSat>=RateThu AND RateSat>=RateFri AND RateSat>=RateSun THEN RateSat 
    WHEN RateSun>=RateMon AND RateSun>=RateTue AND RateSun>=RateWed AND 
     RateSun>=RateThu AND RateSun>=RateFri AND RateSun>=RateSat THEN RateSun 
    END AS MaxRate 
FROM  
    [Room]  
WHERE  
    Id=@Id 

很多打字的，但是这是一个可能的答案。你也可以做到以下几点，这是打字略少：

SELECT Rate, MAX(Rates.Rate) AS MaxRate 
    FROM  
    [Room], 
     (SELECT RateMon AS Rate FROM [Room] WHERE Id=@Id UNION 
     SELECT RateTue AS Rate FROM [Room] WHERE Id=@Id UNION 
     SELECT RateWed AS Rate FROM [Room] WHERE Id=@Id UNION 
     SELECT RateThu AS Rate FROM [Room] WHERE Id=@Id UNION 
     SELECT RateFri AS Rate FROM [Room] WHERE Id=@Id UNION 
     SELECT RateSat AS Rate FROM [Room] WHERE Id=@Id UNION 
     SELECT RateSun AS Rate FROM [Room] WHERE Id=@Id) 
    AS Rates 
    WHERE  
    Id=@Id 

当然，正确的解决方案将正常化您的数据库，使这个没有实际意义，因为一个简单的连接和分组聚集就足够了。

Answer 3

你可以unpivot的日子与union子查询：

select Rate 
,  max(DayRate) 
from (
     select ID, Rate, RateMon as DayRate from Room 
     union all 
     select ID, Rate, RateTue from Room 
     union all 
     select ID, Rate, RateWed from Room 
     union all 
     .... 
     ) as SubQuery 
where ID = @ID 
group by 
     Rate