Oracle “Partition By” Keyword

Question

Can someone please explain what the partition by keyword does and give a simple example of it in action, as well as why one would want to use it? I have a SQL

Answer 1

the over partition keyword is as if we are partitioning the data by client_id creation a subset of each client id

select client_id, operation_date,
       row_number() count(*) over (partition by client_id order by client_id ) as operationctrbyclient
from client_operations e
order by e.client_id;

this query will return the number of operations done by the client_id