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当用户填写表单时，如果LinkedIn Id已经存在，它应该会抛出一个错误，说
LinkedIn Id already exists.。检查是否存在记录并自动填充mysql表中的ID如果用户没有输入
ContactID，表格不保存数据。ContactID是MySQL表中的一个自动递增字段。由于不止一个用户同时在同一个表单上工作，我希望ContactID由MySQL表中的下一个可用编号自动填充。
这里是我的HTML表单代码和下面的PHP代码。如果您需要其他细节进行调试，请询问。
<html>
<body>
<form method="post" action="demo.php">
<link rel="stylesheet" href="contact_css.css">
<!--Create a table -->
<table>
<tr><td><b>Contact Information</b></td>
</tr>
<tr>
<div class="leftside">
<td>ContactID</td>
<td><input type="text" name="ContactID"></td>
</div>
<div class="rightside">
<td>ContactOwner</td>
<!-- <td><input type="text" name="ContactOwner"></td>-->
<td><select name="ContactOwner">
<option value="None">None</option>
<option value="Malik">Malik</option>
<option value="Ankit">Ankit</option>
<option value="Vikrant">Vikrant</option>
</select></td>
</div>
</tr>
<tr>
<div class="rightside">
<td>LeadSource</td>
<td><select name="LeadSource">
<option value="None">None</option>
<option value="Advertisement">Advertisement</option>
<option value="ColdCall">ColdCall</option>
<option value="LinkedIn">LinkedIn</option>
<option value="Web">Web</option>
</select></td>
<!--<td><input type="text" name="LeadSource"></td>-->
</div>
<div class="leftside">
<td>First_name</td>
<td><input type="text" name="First_name"></td>
</div>
</tr>
<tr>
<div class="rightside">
<td>Last_name</td>
<td><input type="text" name="Last_name"></td>
<td>AccountName</td>
<td><input type="text" name="AccountName"></td>
</tr>
<tr>
<td>Title</td>
<td><input type="text" name="Title"></td>
<td>EmailID</td>
<td><input type="text" name="EmailID"></td>
</tr>
<tr>
<td>Industry</td>
<td><input type="text" name="Industry"></td>
<td>Department</td>
<td><input type="text" name="Department"></td>
</tr>
<tr>
<td>Phone</td>
<td><input type="text" name="Phone" required></td>
<td>Mobile</td>
<td><input type="text" name="Mobile"></td>
</tr>
<tr>
<td>Today_date</td>
<td><input type="date" name="Today_date"></td>
<td>LinkedIn</td>
<td><input type="text" name="LinkedIn"></td>
</tr>
<tr>
<td>CallStatus</td>
<td><select name="CallStatus">
<option value="None">None</option>
<option value="AnsweringMachine">AnsweringMachine</option>
<option value="Callback">Callback</option>
<option value="NotInterested">NotInterested</option>
<option value="Prospect">Prospect</option>
<option value="WrongContact">WrongContact</option>
<option value="PerformedInternally">PerformedInternally</option>
<option value="LessThan30Employee">LessThan30Employee</option>
</select></td>
<td>Website</td>
<td><input type="text" name="Website"></td>
</tr>
</table>
<!-- Second table-->
<table>
<tr><td><b>Address Information</b></td>
</tr>
<tr>
<div class="leftside">
<td>Street</td>
<td><input type="text" name="Street"></td>
</div>
<div class="rightside">
<td>OtherStreet</td>
<td><input type="text" name="OtherStreet"></td>
</div>
</tr>
<tr>
<div class="leftside">
<td>City</td>
<td><input type="text" name="City"></td>
</div>
<div class="rightside">
<td>State</td>
<td><input type="text" name="State"></td>
</div>
</tr>
<tr>
<td>Zip</td>
<td><input type="text" name="Zip"></td>
<td>Country</td>
<td><input type="text" name="Country"></td>
</tr>
</table>
<!--Third table-->
<table>
<tr><td><b>Description Information</b></td>
</tr>
<tr>
<td>Description</td>
<td><input type="text" name="Description" class="Description"></td>
</table>
<button type="button">Cancel</button>
<button type="button" class="button2" onclick="window.location.href='fetch_data.php'" />View</button>
<button type="button" class="button3" onclick="window.location.href='exm_list.php'" />Edit</button>
<button type="submit">Add</button>
</form>
< /body>
</html>
PHP代码：
<?php
// create a variable
if (isset($_POST)){
$ContactID=$_POST['ContactID'];
$ContactOwner=$_POST['ContactOwner'];
$LeadSource=$_POST['LeadSource'];
$First_name=$_POST['First_name'];
$Last_name=$_POST['Last_name'];
$AccountName=$_POST['AccountName'];
$Title=$_POST['Title'];
$EmailID=$_POST['EmailID'];
$Industry=$_POST['Industry'];
$Department=$_POST['Department'];
$Phone=$_POST['Phone'];
$Mobile=$_POST['Mobile'];
$Today_date=$_POST['Today_date'];
$LinkedIn=$_POST['LinkedIn'];
$CallStatus=$_POST['CallStatus'];
$Website=$_POST['Website'];
$Street=$_POST['Street'];
$OtherStreet=$_POST['OtherStreet'];
$City=$_POST['City'];
$State=$_POST['State'];
$Zip=$_POST['Zip'];
$Country=$_POST['Country'];
$Description=$_POST['Description'];
}
//create connection
$connect=mysqli_connect('localhost','root','','contacts');
$check="SELECT COUNT(*) FROM contact where ContactID='$_POST[ContactID]' ";
$result=mysqli_query($connect,$check);
$data=mysqli_fetch_array($result, MYSQLI_NUM);
if($data[0] > 1){
echo "LinkedIn id already exists";
}
else {
$newUser="INSERT INTO contact(ContactID,ContactOwner,LeadSource,First_name,Last_name,AccountName,Title,EmailID,Industry,Department,Phone,Today_date,LinkedIn,CallStatus,Website,Street,OtherStreet,City,State,Zip,Country,Description)
VALUES('$ContactID','$ContactOwner','$LeadSource','$First_name','$Last_name','$AccountName','$Title','$EmailID','$Industry','$Department','$Phone','$Today_date','$LinkedIn','$CallStatus','$Website','$Street','$OtherStreet','$City','$State','$Zip','$Country','$Description')";
if (mysqli_query($connect,$newUser))
{
echo "Information Added<br/>";
}
else
{
echo "Error adding user in database, ContactID exists.<br/>";
}
}
请使用[MySQLi的预处理语句（http://php.net/manual/en/mysqli.quickstart.prepared- statement.php）来防止SQL注入。 – PeterMader