How to sort strings as numbers in SQL?

问题

Can anyone tell me how to fix this? My order by is by coursenum (for example, CS 20, CS 25, CS 100 are all course numbers) ascending. It's counting the first digit instead of the whole number though:

-----------------------------------------
Course                              Grade
-----------------------------------------
CS 120 Intro to Java Programming        A
CS 140 Structured Analysis              A
CS 20 Intro to Computers                F
CS 25 Intro to Programming              B

回答1:

The problem here is that your database is doing a string sort, rather than a numeric sort. A computer won't be able to look at that data and infer a semantic sorting order. A string sort is done by taking two strings, and comparing each character until one character comes before another. So, in your example, each of those courses begins with "CS ", but then the 4th character is a numeric character (which is not the same as a numeric type!). the "1"s sort as lower than the "2"s, and then in the "1"s, the "2" sorts lower than the "4", and so on.

To solve this, you'd either need to zero pad the course number ("CS 020") or you'd need a separate numeric column with the course number to sort on.

回答2:

Strip out the non-digital characters and use to_number(),

with t as (
 select 'CS 120 Intro to Java Programming' course from dual
 union
 select 'CS 140 Structured Analysis' course from dual
 union
 select 'CS 20 Intro to Computers' course from dual
 union
 select 'CS 25 Intro to Programming' course from dual
)
select
  course, regexp_replace(course, '[^0-9]', null) n
from
  t
order by
  to_number(regexp_replace(course, '[^0-9]', null))
;

来源：https://stackoverflow.com/questions/4357527/how-to-sort-strings-as-numbers-in-sql

标签

sql

mysql

Oracle

sql-order-by