I MySQL 8+ kan du till exempel använda
SELECT category.ID, category.TITLE, TRIM(jsontable.value) CATEGORY
FROM category
CROSS JOIN JSON_TABLE( CONCAT('["', REPLACE(category.CATEGORY, ',', '","'), '"]'),
"$[*]" COLUMNS( value VARCHAR(254) PATH "$" )
) AS jsontable
ORDER BY category.ID, jsontable.value;