選擇列的基礎上最大值

Question

我有一個表count與屬性

• COUNT1
• COUNT2
• 共3個記錄
• count4
• count5

我想選擇一個具有最大值的列。我怎麼做？

計數代表頁面命中，我想選擇一個具有最大命中並顯示它的列。

Answer 1

您可以使用一個雙重嵌套子查詢

select 
    (select max(count1) 
    from (
    select count1 union all 
    select count2 union all 
    select count3 union all 
    select count4 union all 
    select count5) X) as MaxCount 
from tbl 

Answer 2

有幾種方法，涉及PIVOT或Temp Table，但我認爲最容易理解的是使用Case爲此。

SELECT 
    CASE 
     WHEN count1 >= count2 AND count2 >= count3 AND count1 >= count4 AND count1 >= count5 THEN count1 
     WHEN count2 >= count3 AND count2 >= count4 AND count2 >= count5 THEN count2 
     WHEN count3 >= count4 AND count3 >= count5 THEN count3 
     WHEN count4 >= count5 THEN count4 
     ELSE count5 
    END AS highestCount 

Answer 3

select MAX(max_count) FROM 
    (
    select count1 as max_count from count 
    UNION 
    select count2 as max_count from count 
    UNION 
    select count3 as max_count from count 
    UNION 
    select count4 as max_count from count 
    UNION 
    select count4 as max_count from count 
    ) 

我不會建議使用選擇，因爲它需要很多的時候產生相同的。觸發器會更好