how to append two tables into one in postgresql

Question

I am looking for a way to append two tables in postgresql

table_1 is like

name | age | grade
aaa    20    A
bbb    21    B

And table_2 is like

name | age | grade
ccc    20     C
ddd    22     A

What i am trying to do is append table_2 to table_1, so that table_1 will be

name | age | grade
aaa     20   A
bbb     21   B
ccc     20   C
ddd     22   A

Done these things. Like create a "sample.sql" file and try to run

database_name=# \i /path/to/sample.sql

It resulted in error. The statements in sample.sql file is

select * from table_1
union
select * from table_2
insert into table_1;

I am new to the database thing.

Answer 1

insert into table_1 (name, age, grade)
select name, age, grade
from table_2;