Need Help in Working Javascript and PHP together

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Hello guys!

I need help in working javascript and php together.

 

I have these two tables in my MySQL database:

 

CREATE TABLE `products` (

  `product_id` int(10) unsigned NOT NULL auto_increment,

  `product_code` varchar(10) NOT NULL,

  `product_name` varchar(30) NOT NULL,

  `selling_price` decimal(10,2) unsigned NOT NULL default '0.00',

  PRIMARY KEY  (`product_id`)

);

 

CREATE TABLE `purchase_details` (

  `purchase_detail_id` int(15) unsigned NOT NULL auto_increment,

  `purchase_id` int(10) unsigned NOT NULL,

  `product_id` int(5) unsigned NOT NULL,

  `quantity` decimal(7,2) unsigned NOT NULL,

  `unit_price` decimal(10,3) unsigned NOT NULL default '0.000',

  `unit_discount` decimal(8,3) unsigned NOT NULL default '0.000',

  `net_price` decimal(13,3) NOT NULL,

  `balance` decimal(8,2) NOT NULL,

  PRIMARY KEY  (`purchase_detail_id`)

);

 

 

And in my php file named add_sale, i have this form:

 

$show_form  = "<form name='AddSaleForm' action='add_sale.php' method='post'>

                    <table class=data border=1><thead class=data>";

$show_form .= "<tr><td align=center colspan=4><b>Product Details</b></td></tr>";

$show_form .= "<tr>

<td align=center>Product Name</td>

<td align=center>Selling Price</td>

<td align=center>Qty Available</td>

<td align=center>Qty To Be Sold</td>

</tr></thead><tbody class=data>";

 

for ($i=1; $i<21; $i++) {

$show_form .= "<tr>

        <td align=left><select name='product_id$i' onChange=\"Populate_selling_price_and_quantity_available()\"><option value=>Product Name</option>";

                // select only the products that are non-zero in values in the inventory 

$sql = "SELECT p.product_id, p.product_name

                          FROM products p, purchase_details pd

                          WHERE pd.product_id = p.product_id AND SUM(pd.balance) > 0

                          ORDER BY p.product_name";

$res = mysql_query($sql);

while ($row = mysql_fetch_array($res)) {

show_form .= "<option value=$prow[0]>$prow[1]</option>";

}

$show_form .= "</select></td>

<td align=center><input readonly=1 type=text class=TextBox size=10 name='selling_price$i'></td>

<td align=center><input readonly=1 type=text class=TextBox size=10 name='quantity_available$i'></td>

<td align=center><input type=text class=TextBox size=3 name='quantity_2_b_sold$i' onblur=\"check_if_quantity_2_b_sold_IS_NOT_GREATER_THAN_quantity_available()\"></td>

</tr>";

}

 

$show_form .= "<tr><td align=center colspan=4>

<input type=reset>   

<input onClick=\"EvalAddSaleForm()\" type=button value=Submit></td></tr>";

$show_form .= "</tbody></table></form>";

 

print $show_form;

 

What i need is:

 

1. If I have selected a product in the drop down menu named product_id,

    the Populate_selling_price_and_quantity_available() function will

    a. show the selling price in the uneditable selling_price textbox and

    b. show the quantity available in the uneditable quantity_available textbox.

    // the sql for showing the quantity available:

    "SELECT SUM(balance) FROM purchase_details WHERE product_id = '$selected_product_id_from_drop_down_menu'";

 

2. If i have entered a value in the quantity_2_b_sold textbox,

  the check_if_quantity_2_b_sold_IS_NOT_GREATER_THAN_quantity_available() function will automatically check that its value is not greater than the value in the uneditable selling_price textbox

 

Thank you very much in advanced guys. More power to you all.