Design of a database table

[hmidi slim <hmidi.slim2@xxxxxxxxx>]

I'm trying to design a database table. First of all there are two alternatives:

1-) Divide the table into two tables and make a join.

2-) Design a single table.

1rst alternative:
Create table data_periods(

id serial primary key not null,
period daterange,
project_id integer

)

create table data_periods_info(

id serial primary key not null,

data_periods_id integer,

data_sub_periods daterange,

stock1 integer,

stock2 integer,
CONSTRAINT data_periods_allotment_id_fkey FOREIGN KEY (data_periods_id)
        REFERENCES data_periods (id) MATCH SIMPLE
        ON UPDATE NO ACTION
        ON DELETE NO ACTION

)

The table data_periods contains 1M rows and data_periods_info 5M rows.

I added an index to the table data_periods_info for the column data_periods_id

I execute this query:
select
data_periods.id, 
data_sub_periods,
project_id,
stock1,
stock2
from data_periods
inner join data_periods_info on data_periods_info.data_periods_id = data_periods.id
where data_periods.period && '[2018-07-28, 2018-08-02]'::daterange
and data_sub_periods  && '[2018-07-28, 2018-08-02]'::daterange

I got an execution time of : 1s 300ms

2nd alternative:
create table data_periods_second(

id serial primary key not null,

data_sub_periods daterange,

project_id integer,

stock1 integer,

stock2 integer)

I run this query;
select * from data_periods_second
where data_sub_periods && '[2018-07-28, 2018-08-02]'::daterange

I got such a execution time : 1s

Is it normal to get an execution time when using join relation greatest than the execution time of a table contains million of rows and many columns?