PHP检测用户名是否存在

reg.php

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" />
<link rel="stylesheet" type="text/css" href="css/int.css" />
<script type="text/javascript" src="js/func.js"></script>
<style type="text/css">
td{
    height:30px;
    vertical-align:middle;
    align:center;
}
#myText{
 600px;
}
</style>
<title>注册页面</title>
</head>

<body >

<?php
error_reporting(0);
//不让PHP报告有错语发生。如果不关闭好有类似这的错语 Warning: preg_match() 关闭就不出现了
session_start();
header("Cache-control: private");

$conn = @ mysql_connect("localhost","root","")or die("数据库连接错误");
mysql_select_db("bbs",$conn);
mysql_query("set names utf8");

if($_POST['submit'])
{   
    $username = $_POST["username"];
    
    $sql="select userName  from user_info where userName='$username'";
 //   echo $sql;
    
    $query=mysql_query($sql);
    $rows = mysql_num_rows($query);
    if($rows > 0){
         echo "<script type='text/javascript'>alert('用户名已存在');location='javascript:history.back()';</script>";
    }else{
        $user_in = "insert into user_info (username,pass,sex,qq,email,img) values ('$_POST[username]',md5('$_POST[pass]'),'$_POST[sex]','$_POST[qq]','$_POST[email]','$_POST[img_select]')";        
        //echo $user_in;
        mysql_query($user_in);
        echo "<script type='text/javascript'>alert('写入成功！！');location.href='login.php';</script>";
       
    }

//javascript:history.go(-1)
    
}
?>


<form  action="reg.php" name="reg_form" method="post" onsubmit="return check_reg()">
<table name="reg_table" align="left">
<tr>
    <td>用户：</td><td><input id="username" name="username" class="myText" type="text" maxlength="12" /></td>
</tr>

<tr> <!--性别：0 保密 1 女 2 男-->
     <td > 性别：</td>
     <td>女<input type="radio" value="1" name="sex"/>
         男<input type="radio" value="2" name="sex" />
       保密<input type="radio" value="0" name="sex"  checked/></td>
</tr>

<tr>
    <td>密码：</td><td><input name="pass" class="myText" type="password" onblur="check_len(this)"/><span id="show_pass" style="color:red;"></span></td>
</tr>

<tr>
    <td>重复密码：</td><td><input name="repass" class="myText" type="password" onblur="check_pass(this)" /><span id="show_repass" style="color:red;"></span></td>
</tr>

<tr>
    <td>QQ：</td><td><input type="text" class="myText"  name="qq" onblur="check_qq(this)"/><span style="color:red;" id="show_qq"></span></td>
</tr>

<tr>
    <td>邮箱：</td><td><input type="text" class="myText" name="email"  onblur="check_email(this)"/><span id="show_e" style="color:red;"></span></td>
</tr>

<tr>
    <td height="60">头像：</td>
    <td>
    <select name="img_select" onchange="img_change(this)">
        <option value="101" >女 001</option>
        <option value="102" >女 002</option>
        <option value="103" >女 003</option>
        <option value="104" >女 004</option>
        <option value="105" >男 001</option>
        <option value="106" >男 002</option>
        <option value="107" >男 003</option>
        <option value="108" >男 004</option>
     </select>
     <img src="/bbs/img/101.gif" id="tx_change" style="50px; height:65px;" alt=""/>
    </td>
</tr>

<tr height="20" align="justify">
    <td align="right" ><input type="submit" value="注册" name="submit" style="margin-right:5px;"/></td>
    <td><input type="reset"  value="重置" name="reset" style="margin-left:5px;"/></td>
</tr>

<tr>
    <td  colspan="2">我已有账号现在<a href="login.php">登录</a></td>
</tr>

</table>
</form>
</body>
</html>

func.js

//根据下拉框变换图片
function img_change(thisObj){
    var imgsrc = "/bbs/img/"+ thisObj.value+".gif";
    document.getElementById("tx_change").src=imgsrc;    
}

//检查是否都符合 注册 要求
function check_reg()
{
if(check_len() && check_pass() && check_email() && check_qq())
{
    return true;    
}else{
    return false;
    }
}

//检查密码长度不能少于6
function check_len(thisObj){
    if(thisObj.value.length==0)
    {
        document.getElementById('show_pass').innerHTML="密码不能为空";
        return false;
    }else{
    if (thisObj.value.length<6)
    {
        document.getElementById('show_pass').innerHTML="密码长度不少于6";
        return false;
    }
        document.getElementById('show_pass').innerHTML="";    
        return true;
      }
}

//检查俩次密码输入是否一致
function check_pass(thisObj){
    var psw=document.getElementById('pass');
    if(psw.value.length==0)
    {
        document.getElementById('show_pass').innerHTML="密码不能为空";
        return false;
    }else{
        document.getElementById('show_pass').innerHTML="";    

    if (thisObj.value!=psw.value)
    {
        document.getElementById('show_repass').innerHTML="两次密码输入不正确";
        return false;
    }
        document.getElementById('show_repass').innerHTML="";
        return true;
    }
}

//检查email是否正确
function check_email(thisObj){
    var reg=/^([a-zA-Zd][a-zA-Z0-9_]+@[a-zA-Zd]+(.[a-zA-Zd]+)+)$/gi;    
    var rzt=thisObj.value.match(reg);
    if(thisObj.value.length==0){
        document.getElementById('show_e').innerHTML="Email不能为空";
        return false;
        }else{
    if (rzt==null)
    {
        document.getElementById('show_e').innerHTML="Email地址不正确";
        return false;
    }
        document.getElementById('show_e').innerHTML="";
        return true;
  }

}

//检查qq格式是否正确
function check_qq(thisObj){
    var qq=document.getElementById('qq').value;
    var reg=/^d+$/;
    if(qq.search(reg))
    {
        document.getElementById('show_qq').innerHTML=" QQ 只能为数字";
        return false;
    }else{
        document.getElementById('show_qq').innerHTML="";
        return true ;
        }
    
    
}
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原文地址：https://www.cnblogs.com/mypsq/p/5310881.html