Using if(isset($_POST['submit'])) to not display echo when script is open is not working

Question 1

I have a little problem with my if(isset($_POST['submit'])) code. What I want is some echos and a table to not appear when the script is open but I do want it to show when the submit button for the form has been clicked. The problem is though that when I include the if(isset($_POST['submit'])) function, when I click on the submit button it does not display the echos and the table at all. Why is this and can you help me out with this issue please.

Below is the code:

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>

<title>Exam Interface</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
</head>
<body>

<p><strong>NOTE: </strong>If a search box is left blank, then the form will search for all data under that specific field</p>

<form action="exam_interface.php" method="post" name="sessionform">        <!-- This will post the form to its own page"-->
<p>Session ID: <input type="text" name="sessionid" /></p>      <!-- Enter Session Id here-->
<p>Module Number: <input type="text" name="moduleid" /></p>      <!-- Enter Module Id here-->
<p>Teacher Username: <input type="text" name="teacherid" /></p>      <!-- Enter Teacher here-->
<p>Student Username: <input type="text" name="studentid" /></p>      <!-- Enter User Id here-->
<p>Grade: <input type="text" name="grade" /></p>      <!-- Enter Grade here-->
<p>Order Results By: <select name="order">
<option value="ordersessionid">Session ID</option>
<option value="ordermoduleid">Module Number</option>
<option value="orderteacherid">Teacher Username</option>
<option value="orderstudentid">Student Username</option>
<option value="ordergrade">Grade</option>
</select>
<p><input type="submit" value="Submit" /></p>
</form>

<?php

$username="xxx";
$password="xxx";
$database="mobile_app";

mysql_connect('localhost',$username,$password);

@mysql_select_db($database) or die("Unable to select database");

$sessionid = isset ($_POST['sessionid']) ? $_POST['sessionid'] : "";
$moduleid = isset ($_POST['moduleid']) ? $_POST['moduleid'] : "";
$teacherid = isset ($_POST['teacherid']) ? $_POST['teacherid'] : "";
$studentid = isset ($_POST['studentid']) ? $_POST['studentid'] : "";
$grade = isset ($_POST['grade']) ? $_POST['grade'] : "";
$orderfield = isset ($_POST['order']) ? $_POST['order'] : "";

$sessionid = mysql_real_escape_string($sessionid);
$moduleid = mysql_real_escape_string($moduleid);
$teacherid = mysql_real_escape_string($teacherid);
$studentid = mysql_real_escape_string($studentid);
$grade = mysql_real_escape_string($grade);

switch ($orderfield) {
    case 'ordersessionid': $orderfield = 'gr.SessionId';
    break;
    case 'ordermoduleid': $orderfield = 'm.ModuleId'; 
    break;
    case 'orderteacherid': $orderfield = 's.TeacherId';
    break;
    case 'orderstudentid': $orderfield = 'gr.StudentId'; 
    break;
    case 'ordergrade': $orderfield = 'gr.Grade';
    break;
}

$ordertable = $orderfield;

$result = mysql_query("SELECT * FROM Module m INNER JOIN Session s ON m.ModuleId = s.ModuleId JOIN Grade_Report gr ON s.SessionId = gr.SessionId JOIN Student st ON gr.StudentId = st.StudentId WHERE ('$sessionid' = '' OR gr.SessionId = '$sessionid') AND ('$moduleid' = '' OR m.ModuleId = '$moduleid') AND ('$teacherid' = '' OR s.TeacherId = '$teacherid') AND ('$studentid' = '' OR gr.StudentId = '$studentid') AND ('$grade' = '' OR gr.Grade = '$grade') ORDER BY $ordertable ASC");

$num=mysql_numrows($result);

if(isset($_POST['submit'])){

echo "<p>Your Search: <strong>Session ID:</strong> "; if (empty($sessionid))echo "'All Sessions'"; else echo "'$sessionid'";echo ", <strong>Module ID:</strong> "; if (empty($moduleid))echo "'All Modules'"; else echo "'$moduleid'";echo ", <strong>Teacher Username:</strong> "; if (empty($teacherid))echo "'All Teachers'"; else echo "'$teacherid'";echo ", <strong>Student Username:</strong> "; if (empty($studentid))echo "'All Students'"; else echo "'$studentid'";echo ", <strong>Grade:</strong> "; if (empty($grade))echo "'All Grades'"; else echo "'$grade'"; "</p>";

echo "<p>Number of Records Shown in Result of the Search: <strong>$num</strong></p>";

echo "<table border='1'>
<tr>
<th>Student Id</th>
<th>Forename</th>
<th>Session Id</th>
<th>Grade</th>
<th>Mark</th>
<th>Module</th>
<th>Teacher</th>
</tr>";

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

 echo "<tr>";
  echo "<td>" . $row['StudentId'] . "</td>";
  echo "<td>" . $row['Forename'] . "</td>";
  echo "<td>" . $row['SessionId'] . "</td>";
  echo "<td>" . $row['Grade'] . "</td>";
  echo "<td>" . $row['Mark'] . "</td>";
  echo "<td>" . $row['ModuleName'] . "</td>";
  echo "<td>" . $row['TeacherId'] . "</td>";
  echo "</tr>";
}

echo "</table>";

}

mysql_close();


 ?>

</body>
</html>

Any help will be much appreciated, Thank You.

Question 2

You need to give your submit <input> a name or it won't be available using $_POST['submit']:

<p><input type="submit" value="Submit" name="submit" /></p>

Question 3

Because

$a = array("x" => "0");

if ($a["x"])
  echo "This branch is not executed";

if (isset($a["x"]))
  echo "But this will";

(See also http://hk.php.net/manual/en/function.isset.php and http://hk.php.net/manual/en/language.types.boolean.php#language.types.boolean.casting)

Question 4

In MySQL, backticks quote names, while single quotes create strings. If you have a column called select, MySQL would throw an syntax error when using this name without backticks -- like in SELECT select FROM foo -- as it would interpret it as keyword which may not occur there.
This IF function can be used as a column specification in SELECT statements. See the MySQL reference.
This function returns the value from the default column, if value is the empty string. Else it returns the value from value itself. The result will be called value. See the MySQL reference for details.

Question 5

Include demands that the shape of the query doesn't change. It means that your query must return IQueryable<Match>. GroupBy operator is probably considered as shape changing because it returns IQueryable<IGrouping<TKey, TSource>>. Once the shape of the query changes all Include statements are omitted. Because of that you cannot use Include with projections, custom joins and groupings.

As a workaround you can execute grouping in Linq-to-objects:

var matches = context.matches
                     .Include("Official")
                     .Include("Slot")
                     .Include("MatchParticipants.Team")
                     .Include("Category.Tournament")
                     .Where(m => m.Category.Tournament.TournamentId == tournamentId)
                     .ToList()
                     .GroupBy(m => m.Category);

Edit: As mentioned in comments and in other answer, this is very dangerous workaround which can lead to performance problems. It pulls all records from database to the application and makes the aggregation in the app. It can work in same cases but it is definitely not applicable as generic solution.

Question 6

Using a pipe sends the output (stdout) of the first command, to stdin (input) of the child process (2nd command). The commands you mentioned don't take any input on stdin. This would work, for example, with cat (and by work, I mean work like cat run with no arguments, and just pass along the input you give it):

ls | cat

For your applications, this is where xargs comes in. It takes piped input and gives it as arguments to the command specified. So, you can make it work like:

ls | xargs du -sb

Beware that by default xargs will break its input on spaces, so if your filenames contain spaces this won't work as you want. So, in this particular case, this would be better:

du -sb *

Using if(isset($_POST['submit'])) to not display echo when script is open is not working

Answers

php,mysql,post,if-statement,isset