How to insert an html input array into mysql using PDO

Question

I have an HTML form that has 2 dynamic fields which are:

Answer 1

Assuming the table's name shown in the image you posted in your question ingredient_quantity in your database, and you said you already have the recipe-ID PHP Fiddle

<?php 
    $newid = 'A10';
    //considering this is your table shown in the picture
    $sql = "INSERT INTO ingredient_quantity VALUES";

    for($i = 1 ; $i <= count($_POST['ingredients']) ; $i++){
        $sql .= " (:newid" .$i. ", :ingredient" .$i. ", :quantity" .$i. "),"; 
    }

    // remove the last (,) from the $sql
    $sql = rtrim($sql, ',');
    $sth = $con->prepare($sql);

    // binding parameters 
    for($i = 1 ; $i <= count($_POST['ingredients']) ; $i++){
        $varIng = $_POST['ingredients'][$i];
        $varQnty = $_POST['quantity'][$i];
        $sth->bindParam(':newid' .$i , $newid , PDO::PARAM_STR);
        $sth->bindParam(':ingredient' .$i , $varIng , PDO::PARAM_STR);
        $sth->bindParam(':quantity' .$i , $varQnty , PDO::PARAM_STR);
    }
    $sth->execute();
?>

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EDIT 1:

for the above code I have an error as the ingredients[] array starts from 0 and not 1, the final index of the for loop will be undefined, so work around it make the last for loop like the following:

for($i = 0 ; $i < count($_POST['ingredients']) ; $i++){
        $varIng = $_POST['ingredients'][$i];
        $varQnty = $_POST['quantity'][$i];
        $j = $i + 1;
        $sth->bindParam(':newid' .$j , $newid , PDO::PARAM_STR);
        $sth->bindParam(':ingredient' .$j , $varIng , PDO::PARAM_STR);
        $sth->bindParam(':quantity' .$j , $varQnty , PDO::PARAM_STR);
    }

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EDIT 2: You may try doing it with ? placeholders instead of named placeholders like this PHP Fiddle 2:

//considering this is your table shown in the picture
    $sql = "INSERT INTO ingredient_quantity VALUES";

    for($i = 0 ; $i < count($_POST['ingredients']) ; $i++){
        $sql .= " ( ? , ? , ? ) , "; 
    }

    // remove the last (,) from the $sql
    $sql = rtrim($sql, ',');
    $sth = $con->prepare($sql);

    // binding parameters 
    $j = 1;
    for($i = 0 ; $i < count($_POST['ingredients']) ; $i++){
        $varIng = $_POST['ingredients'][$i];
        $varQnty = $_POST['quantity'][$i];
        $sth->bindValue( $j , $varIng);
        $sth->bindValue( $j + 1, $newid);
        $sth->bindValue( $j + 2, $varQnty);
        $j += 3;
    }
    $sth->execute();