[SQL] GROUP BY VS DISTINCT

Distinct 會等於或比快 Group by ，快的話在於，distinct的欄位剛好用到key

If you don't, then use DISTINCT.

GROUP BY in MySQL sorts results. You can even do:

SELECT u.profession FROM users u GROUP BY u.profession DESC

and get your professions sorted in DESC order.

DISTINCT creates a temporary table and uses it for storing duplicates. GROUP BY does the same, but sortes the distinct results afterwards.

So

SELECT DISTINCT u.profession FROM users u

is faster, if you don't have an index on profession.

http://stackoverflow.com/questions/581521/whats-faster-select-distinct-or-group-by-in-mysql