PHP - Why Long Version Of If Error Fails ?

Php programmers,

I am getting this error:

Fatal error: Uncaught mysqli_sql_exception: No index used in query/prepared statement (null) in C:\xampp\htdocs\test\select_adv.php:70 Stack trace: #0 C:\xampp\htdocs\test\select_adv.php(70): mysqli_stmt_execute(Object(mysqli_stmt)) #1 {main} thrown in C:\xampp\htdocs\test\select_adv.php on line 70

Line 70 is:

	if(mysqli_stmt_execute($stmt) === FALSE)
	

Context:

	if(mysqli_stmt_prepare($stmt,$query))
        {
            mysqli_stmt_bind_param($stmt,'s',$_SESSION['search_column']);
            
            if(mysqli_stmt_execute($stmt) === FALSE)
            {
                printf("Error: %s.\n", mysqli_stmt_error($stmt));
                printf("Error: %d.\n", mysqli_stmt_errno($stmt));
            }
	

This removes the error:

	 if($stmt) === FALSE)
            {
                printf("Error: %s.\n", mysqli_stmt_error($stmt));
                printf("Error: %d.\n", mysqli_stmt_errno($stmt));
            }
	

I still want to know why this works:

	 if($stmt) === FALSE)
{
	

but this doesn't work:

	 if(mysqli_stmt_execute($stmt) === FALSE)
	{
	

Let me know.

Full Code in case you're wondering just what on earth is going on ....

	<?php
//include('error_reporting.php');
error_reporting(E_ALL);
ini_set('error_reporting',E_ALL);//Same as: error_reporting(E_ALL);
ini_set('display_errors','1');
ini_set('display_startup_errors','1');
require('conn.php');
echo __LINE__;
?>
	<form name = "search" method = "POST" action="">
<label for="keywords">Keywords:*</label>
<input type="text" name="keywords" id="keywords" placeholder="Input Keywords" required>
<br>
<label for="search_column">Search in ... ?</label>
<select name="search_column" id="search_column">
<option value="page_url">Page Url</option>
<option value="link_anchor_text">Link Anchor Text</option>
<option value="page_description">Page Description</option>
<option value="keyphrases">Keyphrase</option>
<option value="keywords">Keywords</option>
</select>
<br>
<label for="tos_agreement">Agree to TOS or not ? *</label>
<select name="tos_agreement" id="tos_agreement" required>
<option value="Yes">Yes</option>
<option value="No">No</option>
</select>
<br>
<button type="submit">Submit</button><br>
<button type="submit" value="submit">Submit</button><br>
<input type="submit" value="submit"><br>
<button name=submit value=" ">Submit</button><br>
<br>
<input type="reset">
<br>
</form>
	<?php
session_start();
echo __LINE__;
if($_SERVER['REQUEST_METHOD'] === 'POST')
{
    echo __LINE__;
    if(ISSET($_POST['submit']))
    {
        echo __LINE__;
        if(ISSET($_POST['search_column']))
        {
            $_SESSION['search_column'] = $_POST['search_column'];
            echo $_SESSION['search_column'];
            echo __LINE__;
        }
        
        //Re-write the following 4 lines ...
        mysqli_report(MYSQLI_REPORT_ALL|MYSQLI_REPORT_STRICT);
        $conn = mysqli_connect("localhost","root","","test");
        $conn->set_charset("utf8mb4");
	        //$query = "SELECT page_url,link_anchor_text,page_description,keyphrases,keywords FROM links WHERE $_SESSION['search_column'] = ?";
        $query = "SELECT page_url,link_anchor_text,page_description,keyphrases,keywords FROM links WHERE {$_SESSION['search_column']} = ?";
        //$query = "SELECT page_url,link_anchor_text,page_description,keyphrases,keywords FROM links WHERE " . $_SESSION['search_column'] . " = ?";
        
        $stmt = mysqli_stmt_init($conn);
	        if(mysqli_stmt_prepare($stmt,$query))
        {
            mysqli_stmt_bind_param($stmt,'s',$_SESSION['search_column']);
            
            if(mysqli_stmt_execute($stmt) === FALSE)
            {
                printf("Error: %s.\n", mysqli_stmt_error($stmt));
                printf("Error: %d.\n", mysqli_stmt_errno($stmt));
            }
            
            $result = mysqli_stmt_bind_result($stmt,$page_url,$link_anchor_text,$page_description,$keyphrase,$keywords);
            
            mysqli_stmt_fetch($stmt);
            
            while(mysqli_stmt_fetch($stmt))
            {
                echo "url"; echo "<br>";
                echo "anchor_text"; echo "<br>";
                echo "description"; echo "<br>";
                echo "keyphrases"; echo "<br>";
                echo "keywords"; echo "<br>";
                echo "|";
                echo "<br>";
            }
            
            mysqli_stmt_close($stmt);
            mysqli_close($conn);
        }
        else
        {
            echo "1. QUERY failed!";
        }
	        if(mysqli_stmt_prepare($stmt,$query))
        {
            mysqli_stmt_bind_param($stmt,'sssss',$_POST['page_url'],$_POST['link_anchor_text'],$_POST['page_description'],$_POST['keyphrases'],$_POST['keywords']);
            
            if(mysqli_stmt_execute($stmt) === FALSE)
            {
                printf("Error: %s.\n", mysqli_stmt_error($stmt));
                printf("Error: %d.\n", mysqli_stmt_errno($stmt));
            }
            
            $result = mysqli_stmt_get_result($stmt);
            
            while($row = mysqli_fetch_array($result,MYSQLI_ASSOC))
            {
                $page_url = $row['page_url']; echo $page_url; echo "<br>";
                $link_anchor_text = $row['link_anchor_text']; echo $link_anchor_text; echo "<br>";
                $page_description = $row['page_description']; echo $page_description; echo "<br>";
                $keyphrases = $row['keyphrases']; echo $keyphrases; echo "<br>";
                $keywords = $row['keywords']; echo $keywords; echo "<br>";
                echo "|";
                echo "<br>";
            }
            
            mysqli_stmt_close($stmt);
            mysqli_close($conn);
        }
        else
        {
            die("2. QUERY failed!");
        }
        echo '<pre>' . print_r($_POST, 1) . '</pre>';
        echo $_SESSION['search_column'];
    }
}
echo __LINE__;
	?>