Hello friends,
I am going to show you what exactly difference between all this keywords.
Below screen shot i have 3 different user record, which we are getting with all this queries.
1) User.all.select(:email)
select takes (0.3ms) when find user by email and returns Active record object.
2) User.all.pluck(:email)
pluck also takes (0.3ms) when find user by email and returns email Array.
3) User.all.collect(&:email)
collect takes (0.4ms) when find user by email and returns email Array.
4) User.all.map(&:email)
map takes (0.5ms) when find user by email and returns email Array.
You can also try it on your rails console.
Programmers 