MySQL : Conditional ORDER BY to only one column

Question

Hello and thanks for taking time to read this question.

I am using MySQL, and I want to sort results using ORDER BY to one specific column, but the results must be ordered according an specific criteria to this column. For example, to the following table, I want to ORDER BY 'group', showing first the 9,7,6 'group' items and, in the end 10,8,5 'group' items:

names     group
--------- ------
susanita  10
miguelito 5
mafalda   7
manolito  8
libertad  6
felipe    9
guille    8

thanks in advance.

Answer 1

SELECT* FROM mytable ORDER BY
LOCATE(CONCAT('.',`group`,'.'),'.9.7.6.10.8.5.');

I took your sample data, loaded it into a table called mytable and ran it.

Here are the results:

mysql> use test
Database changed
mysql> drop table if exists mytable;
Query OK, 0 rows affected (0.04 sec)

mysql> create table mytable
    -> (
    ->    names varchar(10),
    ->    `group` int
    -> );
Query OK, 0 rows affected (0.08 sec)

mysql> insert into mytable values
    -> ('susanita',  10),
    -> ('miguelito', 5),
    -> ('mafalda',   7),
    -> ('manolito',  8),
    -> ('libertad',  6),
    -> ('felipe',    9),
    -> ('guille',    8);
Query OK, 7 rows affected (0.09 sec)
Records: 7  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM mytable;
+-----------+-------+
| names     | group |
+-----------+-------+
| susanita  |    10 |
| miguelito |     5 |
| mafalda   |     7 |
| manolito  |     8 |
| libertad  |     6 |
| felipe    |     9 |
| guille    |     8 |
+-----------+-------+
7 rows in set (0.00 sec)

mysql> SELECT * FROM mytable ORDER BY
    -> LOCATE(CONCAT('.',`group`,'.'),'.9.7.6.10.8.5.');
+-----------+-------+
| names     | group |
+-----------+-------+
| felipe    |     9 |
| mafalda   |     7 |
| libertad  |     6 |
| susanita  |    10 |
| manolito  |     8 |
| guille    |     8 |
| miguelito |     5 |
+-----------+-------+
7 rows in set (0.01 sec)

mysql>

Give it a Try !!!

UPDATE 2011-09-06 12:33 EDT

Here is another approach:

SELECT* FROM mytable ORDER BY
IF(FIELD(`group`,9,7,6,10,8,5)=0,99999,FIELD(`group`,9,7,6,10,8,5));

This will force any groups other than 9,7,6,10,8,5 to appear at the very bottom of the query.

UPDATE 2011-09-06 14:39 EDT

mysql> SELECT names, `group`
    -> FROM mytable
    -> WHERE `group` IN (9,7,6,10,8,5)
    -> ORDER BY find_in_set(`group`,'9,7,6,10,8,5');
+-----------+-------+
| names     | group |
+-----------+-------+
| felipe    |     9 |
| mafalda   |     7 |
| libertad  |     6 |
| susanita  |    10 |
| manolito  |     8 |
| guille    |     8 |
| miguelito |     5 |
+-----------+-------+
7 rows in set (0.00 sec)

Hey @Nick, yours works as well against my sample data !!!

Answer 2

Use MySQL's find_in_set() function to do this. It is more concise but less portable than the CASE approach gbn proposed.

For example:

SELECT `names`, `group`
FROM my_table
WHERE `group` IN (9,7,6,10,8,5)
ORDER BY find_in_set(`group`,'9,7,6,10,8,5');

Because it relies on string searching, find_in_set() is useful mainly for ordering on small sets of easily searchable keys, like integers.

Answer 3

Typically (it's asked daily in SO) you'd use a CASE which is standard SQL

ORDER BY
    CASE group
          WHEN 9 THEN 1
          WHEN 7 THEN 2
          WHEN 6 THEN 3
          WHEN 10 THEN 4
          WHEN 8 THEN 5
          WHEN 5 THEN 6
          ELSE 7
    END

I'd be interested to see how this compares over a large dataset to the LOCATE(CONCAT...) method from RolandoMySQLDBA

For a more complex example, see 'Conversion failed' error with ORDER BY CASE expression

Answer 4

You could create it as an ENUM type.

ENUM values are sorted according to the order in which the enumeration members were listed in the column specification. (In other words, ENUM values are sorted according to their index numbers.) For example, 'a' sorts before 'b' for ENUM('a', 'b'), but 'b' sorts before 'a' for ENUM('b', 'a').

So create the ENUM field as ENUM('9','7','6','10','8','5')

Disclaimer: I do not endorse this, because I suspect that your group column needs to be dynamic. I am just mentioning it as an option.