Why does PHP jQuery Ajax give execute error?

I'm trying to delete PHP post using jQuery Ajax but for some reason i'm getting 2 different types of errors.

console.log shows following:

Warning PDO::prepare() expects parameter 1 to be string, object given in ajax_functions.php on line 41

Fatal error Uncaught Error: Call to a member function execute() on bool in ajax_functions.php:43

Does anyone know what causes this?

SCRIPT.JS

 $('.post-remove-btn').on('click', function(e) {

                e.preventDefault();  
                var entered_name = $('.name-input').val();

                $.ajax({
                        method: "POST",
                        url: 'functions/ajax_functions.php',  
                        data: { table1: table, tableNr1: tableNr,  'action': 'remove' },
                        success: function(data) {
                                if(data){
                                     console.log(data);
                                    
                                }else{
                                    alert('error');
                                }
                                
                                
                        },
                        error: function(requestObject, error, errorThrow) {
                                alert('error');
                        }
                });

 });    

AJAX_FUNCTIONS.PHP

<?php


include("../database.php");


// AJAX
if( isset($_POST['action']) ) {
  
    if($_POST['action'] == 'remove'){
        

        $table1 = $_POST['table1'];     
        $tableNr1 = $_POST['tableNr1'];  

        if($table1 == 'post'){

            $sql = $pdo->query('DELETE FROM posts WHERE id = ' . $tableNr1);   
            
            $stmt2 = $pdo->prepare($sql); // PDO::prepare() expects parameter 1 to be string
         
            $result = $stmt2->execute();  // Uncaught Error: Call to a member function execute() on bool

            if($result==true){  
                 echo 'post deleted';
            }

        }elseif ($table1 == 'thread') {
            echo 'thread';
        }
    }
}


?>

Solution:

You already executed the query with $pdo->query(...). You can't use the result as the argument to $pdo->prepare() -- that's supposed to take a SQL string as an argument.

You should just use prepare(), and use a parameter to prevent SQL injection.

if($table1 == 'post'){            
    $stmt2 = $pdo->prepare('DELETE FROM posts WHERE id = :number');
    $result = $stmt2->execute([':number' => $tableNr1]);
    if($result){  
        echo 'post deleted';
    }
} elseif ($table1 == 'thread') {
    echo 'thread';
}