SELECT WHERE <> gives infinite loop

Question

I need to select the records those who not exists in the other table.

Companies

company_id | name      | temp
-----------------------------
         1 | Sony      |    1
         2 | Samsung   |    0
         3 | Apple     |    1

Technologies

technology_id | company_id
--------------------------
            1 |          2
            2 |          1
            3 |          1
            4 |          3
            5 |          6
            6 |          7

In these two tables you see that the companies in the technologies table with id 6 and 7 do not exist in the companies table. I need to select those and insert it into the companies table.

I tried many things, but get stuck in much more things :P

Last thing I tried is this:

$query_str = "
    SELECT company_id
    FROM technologies
";
$query = mysqli_query($con, $query_str);
while ($result = mysqli_fetch_assoc($query)) {
    $comp = $result['company_id'];
    $query_str2 = "
        SELECT *
        FROM companies
        WHERE company_id <> '".$comp."'
    ";
    $query2 = mysqli_query($con, $query_str2);

}

But with this code I get this output: 1 2 ... 1403 1 2 ... 1403 ...

1403 is the amount of records in my company table

Answer 1

To get records those who not exists in the other table just use a simple left join no need for multiple queries

select t.*
from technologies  t
left join companies c on t.company_id = c.company_id
where c.company_id is null

Answer 2

You could try doing the work in the database like this perhaps

select * from technologies where company_id not in ( select company_id from companies )