SELECT *
FROM combination c
LEFT JOIN
option o
ON o.id = SUBSTRING_INDEX(c.combination, '_', 1)
LEFT JOIN
variant v
ON v.id = SUBSTRING_INDEX(c.combination, '_', -1)
SELECT *
FROM combination c
LEFT JOIN
option o
ON o.id = SUBSTRING_INDEX(c.combination, '_', 1)
LEFT JOIN
variant v
ON v.id = SUBSTRING_INDEX(c.combination, '_', -1)