Filter results by Product Type and Sort List by Price (PHP/SQL)

Question

I'm in the process of learning how to create an e-commerce site. I'm trying to figure out how to order product results by price. Code below is a menu list to either filter a specific product category or the option to view all products--the code for that works.

I'm not sure how to add code to "sort by price" (low to high, high to low). I've tried creating a function called priceList and calling inside the function categoryList (which queries the database for which product type or to view all products), but does not work.

    function priceList() {
      $con = getConnection();

     if($pUserCat == "lowToHigh") {
        $sqlQuery = "SELECT Price from Products
         ORDER BY Price ASC";
     } elseif($pUserCat == "highToLow") {
        $sqlQuery = "SELECT Price from Products
         ORDER BY Price DESC";

     // Execute Query -----------------------------           
            $result = mysqli_query($con, $sqlQuery);
      if(!$result) {
       echo "Cannot do query" . "<br/>";
       exit;
      }

      $row = mysqli_fetch_row($result);
      $count = $row[0];

      if ($count > 0) {
       echo "Query works" . "<br/>";
      } else {
       echo "Query doesn't work" ."<br/>";
      }

              // Display Results -----------------------------

      $num_results = mysqli_num_rows($result);

      for ($i=0; $i<$num_results; $i++) {
       $row = mysqli_fetch_assoc ($result);
         // print_r($row);
        echo '<img src="data:image/jpeg;base64,'.base64_encode($row['Image']).'" />';
        echo "Price: " . stripslashes($row['Price']);
      }

      // Close connection
      closeConnection($con);
}

Form

    <!--category and price form ------------------------- -->
    <form action="register_script.php" name="frm" method="post">
        <select name="category" id="category">
            <option value="viewall">View All</option>
            <option value="dress">Dress</option>
            <option value="athletic">Athletic</option>
            <option value="sandals">Sandals</option>
       </select>

      <input type="submit" value="Go" />

  </form>


   <form action="register_script.php" name="frm" method="post">

        <select name="price" id="price">
            <option value="lowToHigh">Low to High</option>
            <option value="highToLow">High to Low</option>
       </select>

       <input type="submit" name="orderPrice" value="orderPrice" />

    </form>
    </div>

PHP

<?php
    function categoryList($pUserCat=false) {
    echo "I am in category list" . "<br/>";

    $con = getConnection(); 

     $sqlQuery = "SELECT * from Products";

    if($pUserCat == "athletic") {
       $sqlQuery = "SELECT * from Products
                    WHERE ProductType='athletic'";
    } elseif ($pUserCat == "dress") {
        $sqlQuery = "SELECT * from Products
                    WHERE ProductType='dress'";
    } elseif ($pUserCat == "sandals") { 
            $sqlQuery = "SELECT * from Products
                    WHERE ProductType='sandals'";
    } elseif ($pUserCat == "viewall") {                 
       $sqlQuery = "SELECT * from Products";
    }

    // Execute Query -----------------------------           
        $result = mysqli_query($con, $sqlQuery);
        if(!$result) {
            echo "Cannot do query" . "<br/>";
            exit;
        }

        $row = mysqli_fetch_row($result);
        $count = $row[0];

        if ($count > 0) {
            echo "Query works" . "<br/>";
        } else {
            echo "Query doesn't work" ."<br/>";
        }

          // Display Results -----------------------------

        $num_results = mysqli_num_rows($result);

        for ($i=0; $i<$num_results; $i++) {
            $row = mysqli_fetch_assoc ($result);
           // print_r($row);
          echo '<img src="data:image/jpeg;base64,'.base64_encode($row['Image']).'" />';
          echo "Price: " . stripslashes($row['Price']);
        }


         // priceList();
        $priceOrder = getPriceBtn(); //$priceOrder holds value of option selected in         
     //price order menu
    priceList($priceOrder);
        // Close connection
        closeConnection($con);

}


function getPriceBtn() {    
    //echo "<br/>"."I am calling getPriceBtn function" . "<br/>";
    $priceBtn = $_POST["orderPrice"];           // price button
    return $price;
    //echo $priceBtn;
}

?>

Answer 1

I think you need to pass the $pUserCat to the function priceList($pUserCat);

A tip, you should have a default query like from high to low and if the other option is selected then run that query:

$sqlQuery = "SELECT Price FROM Products ORDER BY Price DESC";

if($pUserCat == "lowToHigh") {
   $sqlQuery = "SELECT Price FROM Products ORDER BY Price ASC";
}

Also you could re-write this:

$sqlQuery = "SELECT * from Products"; // is this needed?

if($pUserCat == "athletic") {
   $sqlQuery = "SELECT * from Products
                WHERE ProductType='athletic'";
} elseif ($pUserCat == "dress") {
    $sqlQuery = "SELECT * from Products
                WHERE ProductType='dress'";
} elseif ($pUserCat == "sandals") { 
        $sqlQuery = "SELECT * from Products
                WHERE ProductType='sandals'";
} elseif ($pUserCat == "viewall") {                 
   $sqlQuery = "SELECT * from Products";
}

like this categoryList($pUserCat):

if($pUserCat != 'viewall') {
   $sqlQuery = "SELECT * FROM Products WHERE ProductType='%s'";
   $sqlQuery = sprintf($sqlQuery, $pUserCat);
} else {
   $sqlQuery = "SELECT * from Products";
}

Answer 2

Local function variables are not shared. If a function variable is defined within a function, then a function that you call from within that function does not have access to the parent's local variables, which is the very reason they are called "local". You need to pass the variable as a parameter:

When defining:

function priceList( $pUserCat ) {
    ...
}

When calling:

priceList( $pUserCat );