How do I select random rows in MySQL?

Question

mytable

pid name field
=== ==== =====
1    A1   0
2    A2   1
3    A3   1
4    A4   0   
5    A5   0

This is my table structure. Here I want to se

Answer 1

Here is my solution:

SELECT *
FROM `mytable`
WHERE name ='A2'
OR name ='A3'
LIMIT 2
UNION
(SELECT DISTINCT *
FROM `mytable`
WHERE name !='A2'
OR name !='A3'
ORDER BY RAND( ) LIMIT 2) ORDER BY RAND()

Answer 2

Generally, using ORDER BY RAND() is not a good idea. Please read the text by Jan Kneschke, showing why: http://jan.kneschke.de/projects/mysql/order-by-rand/

Answer 3

If you are always selecting all the rows in the table:

SELECT pid, name, field, idx
FROM (
    SELECT pid, name, field,
        @pos := IF(name = 'A3', @idx, @pos),
        @idx := @idx + IF(name = 'A3', 2, 1), idx
    FROM mytable, (SELECT @pos = -1, @idx := 0) dm
    WHERE name <> 'A2'
    ORDER BY RAND()
)
UNION SELECT pid, name, field, @pos + 1 idx
FROM mytable
WHERE name = 'A2'
ORDER BY idx;

If you are not always returning all the rows, thus need to check if A3 was returned to know if A2 should be included:

SELECT pid, name, field, idx
FROM (
    SELECT pid, name, field,
        @pos := IF(name = 'A3', @idx, @pos),
        @idx := @idx + IF(name = 'A3', 2, 1), idx
    FROM mytable, (SELECT @pos = -1, @idx := 0) dm
    WHERE name <> 'A2'
    ORDER BY RAND()
    LIMIT 4
)
UNION SELECT pid, name, field, @pos + 1 idx
FROM mytable
WHERE @pos != -1 AND name = 'A2'
ORDER BY idx;