LEFT JOIN vs IN

Databases
1

I am working on Facebook application with nearly 1 mio users. For each user I need to insert into table a friends list. The friends list is used only in 1 page where items of user friends are shown.

When user register I have two options:

a)

"INSERT INTO friends (userId, friendId) VALUES ".$friendList

$friendList is a string like: ($userId,2343),($userId,dfgdf),($userId,67567),…
and than use

SELECT userId FROM users LEFT JOIN friends ON users.userId=friends.userId

b)

UPDATE users SET friends=$friends

$friendList is a string like: 34534,7634,3456346,834463
and than use

$friends=$db->get_var("SELECT friends FROM users WHERE userId=$userId");
SELECT userId FROM users WHERE userId IN ($friends);

If I use the option a), table friends will be really huge (considering almost every user has more than 200 friends). So which one do you think is better for perfromance?

2

are you absolutely sure about that? only one page? :slight_smile:

use option a

3

at the moment yes, only 1 page. Maybe in future there will be more pages where I will need to show friends data.

I was just worried that the table will be too large.

So option A. Thank you

4

several hundred million rows is large, still not even too large.