MySQL FIND_IN_SET search result needed in original sequence - mysql

Question

I am using FIND_IN_SET in MySQL as below :
SELECT
color, b.id
FROM cards b
where FIND_IN_SET(b.color, 'gold,gold,bronze,silver,silver') > 0
GROUP BY b.id
ORDER BY RAND()
limit 5;
And I get output as below :
However, I want to get cards in the same sequence as in the parameter string supplied to FIND_IN_SET i.e.
gold, gold, bronze, silver, silver
So the first output row should be of gold color, then another gold, then bronze and so on - in the same sequence without any random search.
I cannot have self join as it's a big table.

Answer 1

You will need to do this using a UNION of 3 queries to find random 'gold', 'silver' and 'bronze' medallists, and then order those results using FIELD:
SELECT color, id
FROM (
(
SELECT color, id
FROM cards
WHERE color = 'gold'
ORDER BY RAND()
LIMIT 2
)
UNION ALL
(
SELECT color, id
FROM cards
WHERE color = 'bronze'
ORDER BY RAND()
LIMIT 1
)
UNION ALL
(
SELECT color, id
FROM cards
WHERE color = 'silver'
ORDER BY RAND()
LIMIT 2
)
) m
ORDER BY FIELD(color, 'gold', 'bronze', 'silver')
Demo on SQLFiddle
Here's a way you might implement this as a combination of PHP/MySQL:
$pack_sql_comma_separated = 'gold,silver,gold,gold,silver,gold';
$colors = explode(',', $pack_sql_comma_separated);
$counts = array_count_values($colors);
$sql = "SELECT color, id FROM (";
$subqueries = [];
foreach ($counts as $color => $count) {
$subqueries[] = "(
SELECT color, id
FROM cards
WHERE color = '$color'
ORDER BY RAND()
LIMIT $count
)";
}
$sql .= implode(' UNION ALL ', $subqueries) . ') m';
// run SQL query
// ...
// assume all query results read into $rows according to medal colour, something like this
$rows = array('gold' => array(array('id' => 20),
array('id' => 5),
array('id' => 4),
array('id' => 27)
),
'silver' => array(array('id' => 19),
array('id' => 11)
)
);
//display in required order
foreach ($colors as $color) {
$card = array_shift($rows[$color]);
echo "$color {$card['id']}\n";
}
Demo on 3v4l.org