php - 如何使用php防止同一记录在mysql中插入两次

Question

以下是我为不插入相同数据而编写的代码我想如果记录存在于 mysql 中，那么它应该向我显示错误消息，表明记录已经存在，否则部分应该将记录插入数据库，但它不起作用任何人都可以帮助我吗？非常感谢您的帮助

function addcontact()
    {
        if(isset($_POST['addContact']))
        {
            $officeName = strip_tags($_POST['office_name']);
            $contactName = strip_tags($_POST['contactName']);
            $contactNo = strip_tags($_POST['contactNo']);
            $digitalNo = strip_tags($_POST['digitalNo']);
        $mobileNo = strip_tags($_POST['mobileNo']);

        $check="SELECT * FROM contacts WHERE office_name = '$officeName'";
        if(mysql_num_rows($check) != 0)
         {
            echo "Already in Exists<br/>";
        }else
                     {          
                        $sql = mysql_query("INSERT INTO contacts (office_name, contact_no, 
                          digital_no, mobile_no) VALUES 
                         ('$contactName','$contactNo','$digitalNo','$mobileNo')") or die(mysql_error());
        if($sql)
        {
            header("Location: index.php?admin&done");  exit;
        }
        else
        {
            header("Location: index.php?admin&failed");  exit;  
        }
    }
}
}

Answer 1

你在这里犯了错误。

$check="SELECT * FROM contacts WHERE office_name = '$officeName'";
    if(mysql_num_rows($check) != 0)
     {
        echo "Already in Exists<br/>";
    }

只需添加 mysql_query 即可

$check=mysql_query("SELECT * FROM contacts WHERE office_name = '$officeName'");
    if(mysql_num_rows($check) != 0)
     {
        echo "Already in Exists<br/>";
    }

或者你也可以使用类似

    $name=$_POST['username'];

$q="select * from login where name='$name' ";
$rs=mysql_query($q);
if(mysql_fetch_row($rs)>0)
{
    echo "already exist";
}
else
{
    $msg="done";
}