mySql Max函数返回精确结果

Question

I don't know why i am not getting the exact result

SELECT MAX(MID(order_id,3,20)) As Id FROM `tbl_orders` WHERE `domain_id`=2 
+------------+
|   id       |
+------------+
|  10121452  |
+------------+

Even i tried the same function without MID function

SELECT MAX(order_id) As Id FROM `tbl_orders` WHERE `domain_id`=2 
+------------+
|   id       |
+------------+
| Hy10121452 |
+------------+

any my database have highest order

+--------+------------+
| id     |  order_id  |
+--------+------------+
| 1      | Hy10121452 |
| 2      | Hy10121453 |
| 3      | Hy10121454 |
| 4      | Hy10121455 |
| 5      | Hy10121456 |
| 6      | Hy10121457 |
| 7      | Hy10121458 |
| 8      | Hy10121459 |
| 9      | Hy10121460 |
+--------+------------+

i have to increment in the highest number to generate new order No. Is i am doing something wrong?

Answer 1

Change MAX(MID(order_id,3,20)) to MAX(MID(order_id,3,))

Syntax:from W3School

 SELECT MID(column_name,start[,length]) AS some_name FROM table_name; 

where

column_name   Required. The field to extract characters from
start         Required. Specifies the starting position (starts at 1)
length        Optional. The number of characters to return. If omitted, the MID() function returns the rest of the text

Answer 2

由于您需要最高ID，因此您可以使用order by DESC和limit order by DESC

SELECT order_id As Id FROM `tbl_orders` WHERE `domain_id`=2 ORDER BY order_id DESC LIMIT 1

Answer 3

Problem Solved i just have to rectify Order_id column it contains the duplicate entries. duplicate entries removed and problem solved like a charm.

Answer 4

检查你的数据库 - > table->列数据不包含相同的值如bc1 abc2 abc3 xxx1如果你的系列不同那么结果总是错的