Jak načíst řádky v požadovaném pořadí v mysql

Můžete zkusit toto:

SELECT cat_title
FROM table1
WHERE cat_id IN(21,10,25,4)
ORDER BY (cat_id = 21) DESC, (cat_id = 10) DESC, (cat_id = 25) DESC, (cat_id = 4) DESC;

nebo

SELECT cat_title
FROM table1
WHERE cat_id IN(21,10,25,4)
ORDER BY FIND_IN_SET(cat_id, ('21,10,25,4'));