Shantanu's Blog

Corporate Consultant

October 04, 2005

 

MySQL Case Study - 70

Order Order!!

My current query SELECT * FROM table ORDER BY name is coming with the following resultset:

AIYC 1
AIYC 10
AIYC 11
AIYC 12
AIYC 2
AIYC 3
...
AIYC 8
AIYC 9

I am looking for this:

AIYC 1
AIYC 2
AIYC 3
....
AIYC 8
AIYC 9
AIYC 10
AIYC 11
AIYC 12

I have tried the following:

ORDER BY ord(name)
ORDER BY soundex(name)
ORDER BY lpad(name,5, '0')
ORDER BY name + 0
ORDER BY 0 + name

None have helped.

Can anyone help me out?


http://forums.mysql.com/read.php?10,34908,35959#msg-35959


1) The following query will work only if the number always appears at the fixed position from left. i.e. the number will start from the sixth character from left.

SELECT * FROM table ORDER BY CAST(mid(name, 6, LENGTH(name) -5) AS unsigned)

But how do I implement the query to take the length of name instead of 6 as the total length.
Instead of -5 i think its better to grab the length of name and subtract one


2) The following query solves the problem of measuring the length of the string.

SELECT * FROM table ORDER BY 0+SUBSTRING(name, 6)

But no body knows that the number will always start from the sixth character in the string.
The name can have more then 6 alphanumeric characters. How do I get around that?


3) Another option is to sort on the length of the entire string.

SELECT * FROM Kanwal ORDER BY LENGTH(name), name;

But that won't work if I have data like this...

AIYC 1
AIYC 10
AIYC 2

The second row AIYC 10 will appear *after* AIYC 2 since it has more characters in it.
But actually it should be before it as shown above.
So this query won't work as well.


4) If you have a delimiter separating characters and numbers you can use substring_index.

ORDER BY substring_index(name, ' ', 1), substring_index(name, ' ', -1)+0;

But if you don't have a delimiter (ABC1, ABC2, ABC30, ABC10, AIYC1, AIYC2, AIYC10), then what?


5) So here's one way to sort alphanumeric values without a delimiter - I'm not sure if it's the best.

drop table tmp;
create table tmp (name char(10));
insert into tmp values ('AIYC1'), ('AIYC10'), ('AIYC2'), ('ABC1'), ('ABC2'), ('ABC10'), ('ABC30');
insert into tmp values ('tmp.10'), ('tmp.3'), ('emp-22'),('emp-7'),('emp-6a'),('emp-6b'),(45),(7);

--check the maximum length of the field

select max(length(name)) from tmp;

-- and then write a conditional up to that number

select name from tmp
ORDER BY left(name,
(CASE when substr(name,1) between '0' and '9' then 1
when substr(name,2) between '0' and '9' then 2
when substr(name,3) between '0' and '9' then 3
when substr(name,4) between '0' and '9' then 4
when substr(name,5) between '0' and '9' then 5 ELSE 6 end)-1),
0+substr(name,
CASE when substr(name,1) between '0' and '9' then 1
when substr(name,2) between '0' and '9' then 2
when substr(name,3) between '0' and '9' then 3
when substr(name,4) between '0' and '9' then 4
when substr(name,5) between '0' and '9' then 5 ELSE 6 end);

+--------+
| name |
+--------+
| 7 |
| 45 |
| ABC1 |
| ABC2 |
| ABC10 |
| ABC30 |
| AIYC1 |
| AIYC2 |
| AIYC10 |
| emp-6a |
| emp-6b |
| emp-7 |
| emp-22 |
| tmp.3 |
| tmp.10 |
+--------+

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