如果接收到值isset，则回显输入字段

I have a search form on a webpage which i will create a dynamic page from the content in putted. I have got it to work but there is another one of these forms and there is also selectable data. I want it to only show the hidden fields lines when sku, sku2, txtKeyword2 is set. Please find below what i have tried so far.

<form name="frmSearch" method="get" action="<?=$_SERVER['SCRIPT_NAME']?>">
  <table width="100%">
    <tr>
      <th><h3>Search    </h3>
            <div class="alert-box">Insert Text for alert box</div>
        <input name="txtKeyword" type="text" id="txtKeyword" value="<?=$_GET["txtKeyword"];?>" size="40">
        <?php if(isset($_GET['sku'])) echo '<input type="hidden" name="sku" value="'.$_GET['sku'].'">'?>
        <?php if(isset($_GET['sku2'])) echo '<input type="hidden" name="sku2" value="'.$_GET['sku2'].'">'?>
        <?php if(isset($_GET['txtKeyword2'])) echo '<input type="hidden" name="txtKeyword2" value="'.$_GET['txtKeyword2'].'">'?>
        <input class="alert button" type="submit" value="Search"></th>
    </tr>
  </table>
</form>

All i want is for it not to show the input lines if they are not set. I think i am doing right but i am not sure as i am learning php.

I have also tried the following code which did work but it outputted the following url.

index.php?txtKeyword=giro%25skyline&sku=%09%09<input+type%3D

I know this shouldn't happen but it makes my page work but when i goto enter data in to the other search form it adds part of the input line in to the url. Here is the code that i tried:

<form name="frmSearch" method="get" action="<?=$_SERVER['SCRIPT_NAME']?>">
  <table width="100%">
    <tr>
      <th><h3>Search    </h3>
            <div class="alert-box">Insert text for the alert box</div>
        <input name="txtKeyword" type="text" id="txtKeyword" value="<?=$_GET["txtKeyword"];?>" size="40">
        <input type="hidden" name="sku" value="<?php if(isset($_GET['sku'])) echo ''.$_GET['sku'].'">'?>
        <input type="hidden" name="txtKeyword2" value="<?php if(isset($_GET['txtKeyword2'])) echo ''.$_GET['txtKeyword2'].'">'?>
        <input type="hidden" name="sku2" value="<?php if(isset($_GET['sku2'])) echo ''.$_GET['sku2'].'">'?>
        <input class="alert button" type="submit" value="Search"></th>
    </tr>
  </table>
</form>

I would really like to know what is going on how i can fix it.

Thanks Ryan