此问题在此处已有答案：

Inserting into a mysql table and overwritng any current data（5个答案）
昨天关门了。
我需要一些帮助，让这个代码的工作，使它能够防止重复进入数据库的cname，ccode，crgeno和cvatno。请帮助。

//My DB Code
public function insert($cname, $ccode, $cregno, $cvatno)
    {
        $sql = "INSERT INTO tbl_client (ccode, cname, cregno, cvatno) VALUES (:amcname,:amccode,:amcregno,:amcvatno)";
        $stmt = $this->conn->prepare($sql);
        $stmt->execute(['amcname' => $cname, 'amccode' => $ccode, 'amcregno' => $cregno, 'amcvatno' => $cvatno]);
        return true;
    }

//My action Code
if(isset($_POST['action']) && $_POST['action'] == "insert"){
        $cname = $_POST['amcname'];
        $ccode = $_POST['amccode'];
        $cregno = $_POST['amcregno'];
        $cvatno = $_POST['amcvatno'];
        
        $db->insert($cname, $ccode, $cregno, $cvatno);
         
    }

@Simone：这么做的：

public function insert($cname, $ccode, $cregno, $cvatno)
    {

        $query = $this->conn->prepare("SELECT cname FROM tbl_client WHERE cname = ?");
        $query->bind_param('s',$cname);
        $query->execute();
        $result = $query->get_result();
        $count = $result->num_rows;

        if($count===0){
            $sql = "INSERT INTO tbl_client (ccode, cname, cregno, cvatno) VALUES (:amcname,:amccode,:amcregno,:amcvatno)";
            $stmt = $this->conn->prepare($sql);
            $stmt->execute(['amcname' => $cname, 'amccode' => $ccode, 'amcregno' => $cregno, 'amcvatno' => $cvatno]);
            return true;
        };   
    }

：（还是有问题...