postgresql - Alphanumeric case in-sensitive sorting in postgres

Question

I am new to postrges and want to sort varchar type columns. want to explain the problem with with below example:

table name: testsorting

   order       name
    1            b
    2            B
    3            a
    4            a1
    5            a11
    6            a2
    7            a20
    8            A
    9            a19

case sensitive sorting (which is default in postgres) gives:

select name from testsorting order by name;

    A
    B
    a
    a1
    a11
    a19
    a2
    a20
    b

case in-sensitive sorting gives:

select name from testsorting order by UPPER(name);

      A
      a
      a1
      a11
      a19
      a2
      a20
      B
      b

how can i make alphanumeric case in-sensitive sorting in postgres to get below order:

          a
          A
          a1
          a2
          a11
          a19
          a20
          b
          B

I wont mind the order for capital or small letters, but the order should be "aAbB" or "AaBb" and should not be "ABab"

Please suggest if you have any solution to this in postgres.

Answer 1

My PostgreSQL sorts the way you want. The way PostgreSQL compares strings is determined by locale and collation. When you create database using createdb there is -l option to set locale. Also you can check how it is configured in your environment using psql -l:

[postgres@test]$ psql -l
List of databases
 Name    |  Owner   | Encoding |  Collate   |   Ctype    |   Access privileges
---------+----------+----------+------------+------------+-----------------------
 mn_test | postgres | UTF8     | pl_PL.UTF8 | pl_PL.UTF8 |

As you see my database uses Polish collation.

If you created database using other collation then you can use other collation in query just like:

SELECT * FROM sort_test ORDER BY name COLLATE "C";
SELECT * FROM sort_test ORDER BY name COLLATE "default";
SELECT * FROM sort_test ORDER BY name COLLATE "pl_PL";

You can list available collations by:

SELECT * FROM pg_collation;

EDITED:

Oh, I missed that 'a11' must be before 'a2'.

I don't think standard collation can solve alphanumeric sorting. For such sorting you will have to split string into parts just like in Clodoaldo Neto response. Another option that is useful if you frequently have to order this way is to separate name field into two columns. You can create trigger on INSERT and UPDATE that split name into name_1 and name_2 and then:

SELECT name FROM sort_test ORDER BY name_1 COLLATE "en_EN", name_2;

(I changed collation from Polish into English, you should use your native collation to sort letters like a?c? etc)