What's field should be INDEX in mysql?

Databases
1

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? :frowning:

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

2

try it and see what happens

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

3

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

4

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

5

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