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php怎么判断数据库是否有某个数据

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说明：
逻辑是对数据进行判断，在传过来的数据为空、或者数据库已有一样的数据的情况下，不插入。

那么将这两种情况下的array下面的key赋值，同样对其他数据进行判断，只有所有数据都满足的情况下，才执行插入数据库的操作。

知识点：mysqli_num_rows
mysql_num_rows是PHP语言的中的函数，其表示取得结果集中行的数目。此命令只对SELECT语句有效。要取得被 INSERT，UPDATE 或者 DELETE 查询所影响到的行的数目，用 mysql_affected_rows()。

成果展示：

第一步：建立数据库

第二步、书写代码

<?php
error_reporting(0);
$con = mysqli_connect("localhost","root","","avoid_duplicaton");

if(isset($_POST['insert'])) {
    # code
    $uname = $_POST['uname'];
    $email = $_POST['email'];
    $pass = $_POST['pass'];

    $errors =array();

    $u = "SELECT username FROM new where username='$uname'";
    $uu = mysqli_query($con,$u);

    $e = "SELECT email FROM new where email='$email'";
    $ee = mysqli_query($con,$e);


    if(empty($uname)){
        $errors['u'] = "Username Requirs";
    }else if (mysqli_num_rows($uu) > 0) {
        # code...
        $errors['u'] = "Username Exist";
    }

    if(empty($email)){
        $errors['e'] = "Email Requirs";
    }else if (mysqli_num_rows($ee) > 0) {
        # code...
        $errors['e'] = "Email Exist";
    }

    if(empty($pass)){
        $errors['p'] = "Password Requirs";
    }

    echo count($errors);

    if (count($errors)==0) {
        # code...
        $query="INSERT INTO new(username,email,password) VALUES('$uname','$email','$pass')"; 
        $result =mysqli_query($con,$query);
        if ($result) {
            # code...
            echo "<script>alert('done')</script>";
        }

    }else{
        echo "<script>alert('failed')</script>";
    }
    

}

?>

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                <div class="col-md-3"></div>
                <div class="col-md-6 jumbotron bg-info">
                    <form method="post">
                        <div class="form-group">
                            <label>Username</label>
                            <input type="text" name="uname" placeholder="Enter username" class="form-control" autocomplete="off">
                            <p class="text-daner"><?php if (isset($errors['u'])) echo $errors['u']; ?></p>
                        </div>
                        <div class="form-group">
                            <label>Email</label>
                            <input type="text" name="email" placeholder="Enter email" class="form-control" autocomplete="off">
                            <p class="text-daner"><?php if (isset($errors['e'])) echo $errors['e']; ?></p>
                       
                        </div>
                        <div class="form-group">
                            <label>Password</label>
                            <input type="text" name="pass" placeholder="Enter pasowrd" class="form-control" autocomplete="off">
                            <p class="text-daner"><?php if (isset($errors['p'])) echo $errors['p']; ?></p>
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参考：https://www.youtube.com/watch?v=c4DVJJZ7p64

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