如何在提交时从下拉菜单中保存所选值

<form action="" method="post">

        <?php   echo "<select id='date' name='date' class='input' >"; 
                    echo '<option value="">Please Select Date</option>'?>
                <?php
                        $sql1 = "SELECT Distinct date,day
                                 FROM errorlog order by date";

                        $result1=mysql_query($sql1,$con);
                        if (!$result1)
                            die ("Could not retrieve date" .mysql_error());

                            for ($counter = 0; $row = mysql_fetch_row ($result1); $counter++) 
                                print ("<option value = '$row[0]'>$row[1] - $row[0]</option>");


                    echo "</select>";
                ?> 
</form>

I need to save the selected value from the drop down menu even when submitting, means every time he selects a value form the drop down menu and click submit the value stays on the select

I would suggest getting the data for <select> before outputting it, like that you can separate your SQL and output logic a little and keep things neater.

$sql1 = "SELECT Distinct date,day
         FROM errorlog order by date";

$result1 = mysql_query($sql1,$con);
if (!$result1)
    die ("Could not retrieve date" .mysql_error());

$data = array();
for ($counter = 0; $row = mysql_fetch_row ($result1); $counter++) {
    $data[] = $row;
}

This will fetch the data and save it into $data for now. One worry at a time. Then, if the user submits over POST, the value he submitted will be in $_POST['date']. We can compare that value with one in $data and use HTML's selected="selected" attribute if a row in $data matches it.

if (!empty($_POST['date'])) {
    $user_date = $_POST['date'];
} else {
    $user_date = '';
}

echo '<form ...>'; // etc.

echo '<select name="date">';
foreach ($data as $row) {
    if ($row[0] == $user_date) {
        echo "<option value = '$row[0]' selected='selected'>$row[1] - $row[0]</option>";
    }
    else {
        echo "<option value = '$row[0]'>$row[1] - $row[0]</option>";
    }
}
echo '</select>';

Note that this will issue multiple selected="selected" outputs if the <select> can have the same value multiple times.