更新内连接两个表

Question

** Table Inputs**

(id_inpits, name, quantity_inputs)

Table Outputs `(id_outputs, name_outputs, quantity_outputs, quantity_disponible)

when I want to update the quantity_output , and calculate the quantity_disponbile

knowing that : quantity_disponbile = quantity_inputs - quantity_output

I tried with :

if(!empty($_POST['do'])) {

    $m_id = $_POST['id_output'];

    $quantity_outputs = $_POST["quantity_outputs"];

    $sql = $db->query("UPDATE outputs AS o INNER JOIN inputs As i ON i.id_input = o.inputs_id  SET o.quantity_dispo = 'select quantity_inputs from inputs - FROM (select quantity_outputs from outputs )', o.quantity_outputs = '$quantity_outputs'  WHERE o.id_output =' $m_id'"); 

    if(!$sql) {
        die(mysql_error());
    }
}

Answer 1

One suggestion: quantity_disponbile is supposed a calculated field from both table. So split the logic into two: one select query and one update query. The update query just need to update the quantity_output, and the select query can be like:

select 
  i.quantity_inputs -  o.quantity_output = quantity_disponible
from output o 
    inner join input i on i.id_inpits = o.inputs_id

I don't correct the typo anyway