PHP dropdown search result selecting wrong input - php

Question

I have made a dropdown search form that is auto populated by my database content. The voices in the table would be for example types of woods with varing dimensions.
So there are repeatable wood names with diverse data.
To avoid repetition the dropdown is populated with wood types combined to be selected then displayed with all their variants.
The problem is, upon selecting an input, the results are of the item listed above and not the one selected.
<form action="search2.php" method="POST">
<select name="finit" onchange='this.form.submit()'>
<?php
include("connect.php");
$query = "SELECT finit FROM prime";
$info = mysqli_query($conn, $query);
$finit = '';
echo "<option value=\"\">Selezione Materiale</option>";
while($row = $info->fetch_assoc()){
if($row['finit'] != $finit) {
echo "<option value=\"$finit\">" . $row['finit'] . "</option>";
$finit = $row['finit'];
}
}
?>
</select>
<noscript><input type="submit" value="Submit"></noscript>
</form>

Answer 1

Since there are many variants(dimensions) associated with a single wood type, you have to first take the wood type as input from user(via dropdown list), and probably then you may want to display all possible variants(dimensions) of that particular wood type.
So, change the SQL query in the following way,
$query = "SELECT DISTINCT finit FROM prime";
and the while loop in the following way,
while($row = $info->fetch_assoc()){
$output = "<option value='" . $row['finit'] . "'";
if($row['finit'] == $_POST['finit']){
$output .= " selected='selected'";
}
$output .= ">" . $row['finit'] . "</option>";
echo $output;
}

Answer 2

Try this but change if condition according your default value and sql value should be match.
<form action="search2.php" method="POST">
<select name="finit" onchange='this.form.submit()'>
<?php
include("connect.php");
$query = "SELECT finit FROM prime";
$info = mysqli_query($conn, $query);
$finit = '';
?>
<option value="">Selezione Materiale</option>;
<?php
while($row = $info->fetch_assoc()){
if($row['finit'] == $finit) {
$selected = 'selected';
}else{
$selected = '';
$finit = $row['finit'];
}
?>
<option value="<?php echo $finit ?>" <?php echo $selected ?>><?php echo $row['finit']?></option>
<?php } ?>
</select>
<noscript><input type="submit" value="Submit"></noscript>
</form>