使用数据库中的值进行计算

I'm better at design but i need to do this and cant figure it out how to do it so ill explain the problem:

So I have this table:

And this one:

1. I want to do is to calculate the sum of the iliquido from the 1st table and put the result at total_iliquido form the 2nd table where id_proposta is equal in both tables;

2. Take the values from total_iliquido and calculate with desconto (discount) and put the value on subtotal;

3. Take subtotal value and calculate with iva and put the result in total;

And that it can someone explain me how to do it please, really need your help guys. So as required here it is the Struct of database:

1st table:

2nd table:

And the connections I made:

So thats all i hope it help.

I didn't test this, but you might get the idea.

UPDATE table2 t2
INNER JOIN(
   SELECT id_proposta, SUM(iliquido) as total
   FROM table1
   GROUP BY id_proposta
) x ON table2.id_proposta = table1.id_proposta
SET table2.total_iliquido = x.total, 
    table2.subtotal = table2.total_iliquido-table2.discount, 
    table2.total=table2.subtotal+table2.iva

EDIT:

To execute this query using php, you can use the following code:

<?php
    $link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
    if (!$link) {
        die('Fail: ' . mysql_error());
    }
    echo 'Success';

    $query = "...";
    $result = mysql_query($query);
    if (!$result) {
        die('Invalid query: ' . mysql_error());
    }

    mysql_close($link);
?>

UPDATE propostas t2
INNER JOIN(
   SELECT id_proposta, SUM(iliquido) as total
   FROM proposta_print
   GROUP BY id_proposta
) x ON t2.id_proposta = x.id_proposta
SET t2.total_iliquido = x.total, 
    t2.subtotal = t2.total_iliquido*t2.desconto/100, 
    t2.total = (t2.subtotal*t2.iva/100)+t2.subtotal

A fix for the one on the top, Thanks for your help Stefan Manciu.