MySQL中VARCHAR字段的数值计算

Question

我有一个（简化的）结果表：

id | Result1 | Result2 | Progress
---------------------------------
1  | 1b      | 3c      | NULL
2  | 2c      | 2a      | NULL
3  | 3c      | 2b      | NULL
4  | P3      | 2c      | NULL
5  | 2c      | A       | NULL

我想根据Result1和Result2列的数字部分（始终是第一个字符）之间的差异来填充Progress列。如果任一结果列的第一个字符不是数字，则Progress列应为NULL。

因此上表的结果应为

3c - 1b = 2
2a - 2c = 0
2b - 3c = -1
2c - P3 = NULL
A - 2c = NULL

感谢您的帮助。

Answer 1

使用CASE AND LEFT()

尝试此操作

SELECT *,
(CASE WHEN
LEFT(Result1 ,1) - LEFT(Result2 ,1) >=0 OR 
LEFT(Result1 ,1) - LEFT(Result2 ,1) <=0
THEN LEFT(Result1 ,1) - LEFT(Result2 ,1)
ELSE NULL END ) `result`
FROM table

编辑

首先检查第一个值是否为数字然后计算

SELECT *,

(CASE WHEN

CONCAT('',LEFT(Result1 ,1) * 1)  =0 THEN NULL

WHEN CONCAT('',LEFT(Result2 ,1) * 1)  =0 THEN NULL

WHEN LEFT(Result2 ,1) - LEFT(Result1 ,1) >=0 OR 

LEFT(Result2 ,1) - LEFT(Result1 ,1) <=0

THEN LEFT(Result2 ,1) - LEFT(Result1 ,1)

ELSE NULL END ) `result`

FROM `progress`

LEFT(str,len)

See working fiddle

Answer 2

UPDATE table
   SET Progress = IF(Result1 RLIKE '^[0-9]' AND Result2 RLIKE '^[0-9]', Cast(Result1 AS SIGNED) - Cast(Result2 AS SIGNED), NULL);

Answer 3

感谢那些回复的人，这里的快速反应使我指出了正确的方向 - 这就是我想出的：

UPDATE mytable SET Progress =
    CASE
        WHEN CAST(Result1 AS SIGNED) > 0 AND CAST(Result2 AS SIGNED) > 0
            THEN CAST(Result2 AS SIGNED) - CAST(Result1 AS SIGNED)
        ELSE NULL
    END

Answer 4

update table_name
set progress=if(left(Result2,1)regexp'[:alpha:]'=1,null,left(Result2,1))-if(left(Result1,1)regexp'[:alpha:]'=1,null,left(Result1,1)) ;