MySQL总和基于col值

Question

我有这张桌子：

+----+--------+-------+
| id | fruit  | a-b-c |
+----+--------+-------+
| 1  | orange | a     |
+----+--------+-------+
| 2  | banana | c     |
+----+--------+-------+
| 3  | orange | c     |
+----+--------+-------+
| 4  | orange | a     |
+----+--------+-------+
| 5  | orange | b     |
+----+--------+-------+

现在，我想根据sum值a-b-c，a=1和b=2列出所有水果和c=3。所以，这将是我想要的结果：

+--------+-----+
| fruit  | sum |
+--------+-----+
| banana | 3   |
+--------+-----+
| orange | 7   |
+--------+-----+

我很确定我应该使用case，但我不知道如何总结它们。我脑子里有这样的事情：

SELECT
    fruit,
    sum(a-b-c)
    CASE
        WHEN a-b-c = 'a' THEN +=1
        ELSE
    CASE
        WHEN a-b-c= 'b' THEN +=2
        ELSE
    CASE
        WHEN a-b-c= 'c' THEN +=3

    END AS sum

FROM tbl_fruits
GROUP BY fruit;

Answer 1

您可以使用条件聚合：

SELECT fruit, SUM(CASE `a-b-c`
                     WHEN 'a' THEN 1
                     WHEN 'b' THEN 2
                     WHEN 'c' THEN 3
                  END) AS total 
FROM tbl_fruits
GROUP BY fruit;

的 SqlFiddleDemo

输出：

╔═════════╦═══════╗
║ fruit   ║ total ║
╠═════════╬═══════╣
║ banana  ║     3 ║
║ orange  ║     7 ║
╚═════════╩═══════╝

或者使用ELT/FIELD：

SELECT fruit, SUM(ELT(FIELD(`a-b-c`,'a','b','c'),1,2,3)) AS total 
FROM tbl_fruits
GROUP BY fruit;

的 SqlFiddleDemo2