Fifo calculation in PHP

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PHP

Please help me let me explain with this.....

purchase table

id purchase_id product_id qty net_unit_cost created_at

1 1 1 10 10 2022-10-10
2 2 1 15 12 2022-10-10

Sale table

sale_id product_id qty net_unit_price created_at

1 1 11 15 2022-10-10

in this, if i sold '11' units then how can i subtract from the rows to get remaining units? i've to subtract '10' units from first row and '1' unit from second row. Please help how to calculate fifo in php

What I have tried:

<?php

// stock_outcomes
$db = mysqli_connect('localhost','root','','pos1010');
$sql = mysqli_query($db,"SELECT * FROM `product_sales` WHERE product_id=1003");


while($mas = mysqli_fetch_array($sql)){
    
       echo    $OutcomeId=$mas[0];
echo "</br>";
        echo   $OutcomeBarCode=$mas[2];
echo "</br>";
        echo   $OutcomeQuantity=$mas[6]; 
    





/* - Start code */
if ($OutcomeQuantity > 0) {
$sql1 = mysqli_query($db,"SELECT * FROM `product_purchases` WHERE qty>0 and product_id=1003 order by id asc");
$mas1 = mysqli_fetch_assoc($sql1);

while($mas1 = mysqli_fetch_array($sql1)){
    //filing stock_outcomes_fifo 

        echo $IncomeId = $mas1[0];
        echo "</br>";
        echo $IncomeQuantity = $mas1[6];
        echo "</br>";
       echo $IncomeUnitPrice = $mas1[9];
       echo "</br>";
        echo $IncomeLeftv = $mas[6];

         $OutcomePart = min($OutcomeQuantity, $IncomeLeftv);
        $FifoLeftv = $IncomeQuantity - $OutcomeQuantity; 
        $FifoCost = $IncomeUnitPrice * $OutcomePart;

         $ins=mysql_query("INSERT INTO `stock_outcomes_fifo` (BarCode,IncomeId,OutcomeId,OutcomePart,UnitPrice,Leftv,Cost) VALUES ($OutcomeBarCode, $IncomeId, $OutcomeId, $OutcomePart, $IncomeUnitPrice, $FifoLeftv, $FifoCost)");      

        $upd = mysqli_query($db,"UPDATE `product_purchases` SET qty = ".$FifoLeftv." WHERE Id = ".$IncomeId."");

        $OutcomeQuantity -= $OutcomePart;
        if ($OutcomeQuantity <= 0) break;
    }

    // $OutcomeCostQuery =mysqli_query($db, "select sum(Cost) as summ from stock_outcomes_fifo where OutcomeId = ".$OutcomeId."");
    // $OutcomeCost = mysql_query($OutcomeCostQuery);
    // $OutcomeCostResult = mysql_fetch_array($OutcomeCost);        
    // mysql_query("UPDATE `stock_outcomes` SET Cost = ".$OutcomeCostResult["summ"]." WHERE Id = ".$OutcomeId."");
}
 /* - Finish code */
}
?>