在ORDER BY语句中计算CASE

Question

不幸的是，我的SQL非常生疏。我现在有一个说法是这样的：

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; 

该查询正确查找最相似的项目到field1，field2，field3分别为A，B和C的“理想”。但是，我也希望能够找到“匹配”字段的数量。看起来我应该能够很容易地得到它，因为我已经在执行该计算，但是我不确定没有另一个子查询。

任何帮助将不胜感激！

Answer 1

修订

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 

在这种特殊情况下（的MySql），你可以根据match_count使用替代CASE与(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 

我们限制结果集HAVING条款

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 

这里是SQLFiddle演示上述所有查询