what's field should be INDEX in mysql?

[phpguru]

today, i checked my slow query log and saw lots of slow queries.

it's looks like:

SELECT uid,uname FROM usertbl WHERE country='us' ORDER BY lastlogin DESC LIMIT 0,20;

i INDEXED country field.
so should i index lastlogin field?

and one more question, should i use DISTINCT or GROUP BY to filter duplicate records?

[r937]

i INDEXED country field.
so should i index lastlogin field?

try it and see what happens

and one more question, should i use DISTINCT or GROUP BY to filter duplicate records?

in general, yes

but ~not~ in this case!

if you are getting duplicates from the query that you posted, then you have some pretty serious issues

[oddz]

Assuming uid is the primary key and uname is unique you should not have duplicates.

[phpguru]

if you are getting duplicates from the query that you posted, then you have some pretty serious issues

i mean, DISTINCT and GROUP BY, which take more a lot of resources?

[r937]

i mean, DISTINCT and GROUP BY, which take more a lot of resources?

it's not a question of resources, it's a question of why do you allow duplicates to occur in the first place?