General Optimization Doubt

let me explain the scenario first

say table1 has columns col1, col2 and col3
where col1 and col2 together is PK

and col1 is same for for entire table and col2 is unique (well some may get doubt why to use col+col2 for pk when col2 alone is unique, to clarify this doubt, we have two dbs where in one db col1 does not repeat (in other words there are multiple dbs created based on this col1) and in other db it repeats (all dbs merged together))

sample data
col1--col2
==========
a--1
a--2
a--3
a--4
a--5
a--6
a--7
.
.
. so on

now my question, does both of the below queries takes same time

ex1:
select * from tabel1
select * from tabel1 where col1 = 'a'

in other words, does WHERE clause has any effect in performance when the column used in the query will always the same value with what it is compared?

does it has any effect when i join also?

ex2:
select a.*
from tabel1
inner join tabel2 a
on a.col1 = b.col1
and a.col2 = b.col2

select a.*
from tabel1
inner join tabel2 a
on a.col2 = b.col2 -- note: col1 is not used in join

and please explain how it is same/different