MYSQL自然排序不符合预期

Question

Natural sorting isn't behaving as expected on a query. I don't understand why. Having looked at this site http://www.copterlabs.com/blog/natural-sorting-in-mysql/ , the method works for the most part. However, the alpha part of the 'code' means sorting occurs in an odd way.

Result

M1
..
M3
P1
..
P3
M10
..
M19
P10
..
P19

Expected

M1
..
M3
M10
..
M19
P1
..
P3
P10
..
P19

Code

'SELECT * FROM stock ORDER BY LENGTH(code), code';

Answer 1

You sort first by the length of the field. Of course that mixes the result in the wrong way. Try splitting the alphanumeric values and the numbers

SELECT * FROM stock 
ORDER BY substr(code, 1, 1), 
         substr(code, 2, 99) * 1

*1 converts the string into a number. You could also use cast(substr(code, 2, 99) as signed)