SQL查詢 - 在不同的項目比較兩個項目

Question

嗨，我是一個牛逼到SQL代碼，並懷疑這是可能得到的輸出： -

 
**EVT John Paul Difference** 
A1  1  2  -1 
A2  2  3  -1 

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從下面的數據源。

 
**EVT PERS RANK** 
A1  John 1 
A1  Paul 2 
A1  Ringo 3 
A1  George 4 
A2  Ringo 1 
A2  John 2 
A2  Paul 3 
A2  George 4 

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Answer 1

SELECT 
     EVT, 
     MAX(CASE WHEN Pers='John' THEN Rank END) AS John, 
     MAX(CASE WHEN Pers='Paul' THEN Rank END) AS Paul, 
     MAX(CASE WHEN Pers='John' THEN Rank END) - 
        MAX(CASE WHEN Pers='Paul' THEN Rank END) as Difference 
FROM YourTable 
WHERE Pers IN ('John','Paul') 
GROUP BY EVT