I would like to know how fast is SELECT * FROM user_table WHERE email = 'test@gmail.com'
is this O(1) or O(n)?
how does sql search for a particular row?
>Solution :
If there is no index on "email" column, the search complexity is O(N).
If there was hash-based index on an "email" column, then the search could be performed in O(1).
However in real DB engines the indices are usually tree-based (as they enable quick search not for equality only, but also for "greater/less than" conditions).
For binary trees the search complexity is O(log N) so in most cases index on "email" column results in this.