SQL，带小数点输入的varchar字段= ORDER BY未正确排序

Question

So i have a table with a VARCHAR field. It is used to sort a lot of decimals value:

Let's say i have the following entries in my VARCHAR field:

• 9.99
• 263.28
• 9.98

Let's say I want to display all entries using ORDER BY varchar DESC. The result would be:

• 9.99
• 9.98
• 263.28

When obviously 263.28 should be the first one. What's wrong ?

Answer 1

If you have all decimal values in varchar field then just convert it to decimal and then apply order by clause. I have not much idea about mysql data type and convert function, but in MS SQL you can convert it to decimal like

ORDER BY CAST(field AS DECIMAL(18,2)) DESC

UPDATE :

Yes, in MySQL also there is cast function : http://dev.mysql.com/doc/refman/5.0/en/cast-functions.html

Answer 2

If you order by a varchar column, mysql will sort alphabetically. The first character "2" comes before "9". That's why you get the order you see. Cast the varchar column to decimal in the order by clause and it should work as you expect.

Alternatively, you could update "9.99" to "009.99" and so on so that all the rows have the same number of characters. Then the alphabetical sort will match the numerical sort. I'm not suggesting you actually use that as a solution - it just shows you how things work in the database.