MariaDB 10.1 Order By + Limit inconsistencies

Question

When running an order by query with a limit on MariaDB 10.1.18, I get back a wrong order.

Observe the query without the LIMIT statement:

select advert_id, published, id from vacancies order by published asc;

+-----------+-----------+----+
| advert_id | published | id |
+-----------+-----------+----+
|    328377 |         0 | 70 |
|    328844 |         0 | 80 |
|    325263 |         0 | 41 |
|    325774 |         0 | 40 |
|    325775 |         0 | 39 |
|    325929 |         0 | 38 |
|    325885 |         0 | 37 |
|    325901 |         0 | 36 |
|    325920 |         0 | 35 |
|    325917 |         0 | 34 |
|    325922 |         0 | 33 |
|    325889 |         0 | 32 |
|    325927 |         0 | 31 |
|    325238 |         0 | 43 |
|    325244 |         0 | 45 |
|    328365 |         0 | 71 |
|    328446 |         0 | 72 |
|    328362 |         0 | 68 |
|    323602 |         0 | 55 |
|    324250 |         0 | 54 |
|    324254 |         0 | 53 |
|    324911 |         0 | 52 |

With the LIMIT statement:

select advert_id, published, id from vacancies order by published asc limit 10;

+-----------+-----------+----+
| advert_id | published | id |
+-----------+-----------+----+
|    327830 |         0 |  1 |
|    326865 |         0 | 18 |
|    327328 |         0 |  9 |
|    326877 |         0 | 16 |
|    326783 |         0 | 21 |
|    326779 |         0 | 17 |
|    326774 |         0 | 15 |
|    326864 |         0 | 20 |
|    326788 |         0 | 14 |
|    326767 |         0 | 19 |
+-----------+-----------+----+

The order by on published is different in both queries.

For comparison, I ran the same queries on MariaDB 5.5.50 and found the order by + limit correctly returns the same result as the order by query. So from what I understand is that this issue is MariaDB specific, and only exists on newer versions.

Additionally I also ran the same queries, but ordering on a varchar field with a lot of different values, in that case the order was correct. So I'm thinking the problem only applies to ordering with limit on a field that has a lot of the same values.

Does anyone know if there is a way around this? Perhaps a setting in MariaDB?

FYI:

Table structure:

+------------------+------------------+------+-----+---------+----------------+
| Field            | Type             | Null | Key | Default | Extra          |
+------------------+------------------+------+-----+---------+----------------+
| id               | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| advert_id        | int(11)          | YES  |     | NULL    |                |
| published        | tinyint(1)       | NO   |     | 0       |                |
| (other fields omitted)

Explain on query:

explain select advert_id, published, id from vacancies order by published asc;
+------+-------------+-----------+------+---------------+------+---------+------+------+----------------+
| id   | select_type | table     | type | possible_keys | key  | key_len | ref  | rows | Extra          |
+------+-------------+-----------+------+---------------+------+---------+------+------+----------------+
|    1 | SIMPLE      | vacancies | ALL  | NULL          | NULL | NULL    | NULL |   52 | Using filesort |
+------+-------------+-----------+------+---------------+------+---------+------+------+----------------+

explain select advert_id, published, id from vacancies order by published asc limit 10;
+------+-------------+-----------+------+---------------+------+---------+------+------+----------------+
| id   | select_type | table     | type | possible_keys | key  | key_len | ref  | rows | Extra          |
+------+-------------+-----------+------+---------------+------+---------+------+------+----------------+
|    1 | SIMPLE      | vacancies | ALL  | NULL          | NULL | NULL    | NULL |   52 | Using filesort |
+------+-------------+-----------+------+---------------+------+---------+------+------+----------------+

Version with order by issue:

mysql  Ver 15.1 Distrib 10.1.18-MariaDB, for debian-linux-gnu (x86_64) using readline 5.2

Version without order by issue:

mysql  Ver 15.1 Distrib 5.5.50-MariaDB, for debian-linux-gnu (x86_64) using readline 5.2

Answer 1

You do not specify which ten first rows you want to obtain. As there are a lot of rows for which published equals 0 MariaDB is free to choose some of them. If you want a specific order try:

SELECT advert_id, published, id FROM vacancies ORDER BY published asc, id LIMIT 10;