在ORDER BY語句中計算CASE

Question

不幸的是，我的SQL非常生疏。我現在有一個說法是這樣的：

SELECT field1, field2, field3 FROM table_name WHERE 
    field1 = 'A' OR field2 = 'B' OR field3 = 'C' ORDER BY 
     CASE WHEN field1 = 'A' THEN 1 ELSE 0 END + 
     CASE WHEN field2 = 'B' THEN 1 ELSE 0 END + 
     CASE WHEN field3 = 'C' THEN 1 ELSE 0 END 
    DESC LIMIT 1; 

該查詢正確查找最相似的項目到field1，field2，field3分別爲A，B和C的「理想」。但是，我也希望能夠找到「匹配」字段的數量。看起來我應該能夠很容易地得到它，因爲我已經在執行該計算，但是我不確定沒有另一個子查詢。

任何幫助將不勝感激！

Answer 1

修訂

SELECT field1, field2, field3, 
     CASE WHEN field1 = 'A' THEN 1 ELSE 0 END + 
     CASE WHEN field2 = 'B' THEN 1 ELSE 0 END + 
     CASE WHEN field3 = 'C' THEN 1 ELSE 0 END match_count 
    FROM table_name 
WHERE field1 = 'A' OR field2 = 'B' OR field3 = 'C' 
ORDER BY match_count DESC 

在這種特殊情況下（的MySql），你可以根據match_count使用替代CASE與(fieldX = 'N')

SELECT field1, field2, field3, 
     (field1 = 'A') + (field2 = 'B') + (field3 = 'C') match_count 
    FROM table_name 
WHERE field1 = 'A' OR field2 = 'B' OR field3 = 'C' 
ORDER BY match_count DESC 

我們限制結果集HAVING條款

SELECT field1, field2, field3, 
     (field1 = 'A') + (field2 = 'B') + (field3 = 'C') match_count 
    FROM table_name 
WHERE field1 = 'A' OR field2 = 'B' OR field3 = 'C' 
HAVING match_count > 1 
ORDER BY match_count DESC 

這裏是SQLFiddle演示上述所有查詢