Cannot add or update a child row: a foreign key constraint fails (`kims`.`question`,

Hi sir i want to transform the data of one table into another through foreign key but the following error come to my browser

Cannot add or update a child row: a foreign key constraint fails (`kims`.`question`, CONSTRAINT `fk_question_subject` FOREIGN KEY (`sub_code`) REFERENCES `subject` (`subject_code`) ON DELETE NO ACTION ON UPDATE NO ACTION)

Here is my code and data base structure.

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 CREATE TABLE IF NOT EXISTS `subject` (

  `subject_code` int(11) NOT NULL AUTO_INCREMENT,

  `Name` text,

  PRIMARY KEY (`subject_code`)

) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=105 ;
 
--

-- Dumping data for table `subject`

--
 
INSERT INTO `subject` (`subject_code`, `Name`) VALUES

(101, 'computer sciense'),

(102, 'Maths'),

(103, 'English'),

(104, 'Chemistry');
 
*********************************************************
 
and the question table is:
 
CREATE TABLE IF NOT EXISTS `question` (

  `question_id` int(11) NOT NULL AUTO_INCREMENT,

  `question` text,

  `weight` int(11) DEFAULT NULL,

  `sub_code` int(11) NOT NULL,

  PRIMARY KEY (`question_id`,`sub_code`),

  KEY `fk_question_subject` (`sub_code`)

) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=205 ;
 
--

-- Dumping data for table `question`

--
 
--

-- Constraints for dumped tables

--
 
--

-- Constraints for table `question`

--

ALTER TABLE `question`

  ADD CONSTRAINT `fk_question_subject` FOREIGN KEY (`sub_code`) REFERENCES `subject` (`subject_code`) ON DELETE NO ACTION ON UPDATE NO ACTION;

Here is my code:

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<?php
 
session_start();
 
 include("conn.php");

     connect();

if($_GET['action']=="add")

{
 
//$sub_code=$_POST['sub_code'];

$sub_name=$_POST['sub_name'];
 
$result=mysql_query("insert into subject values('','$sub_name')") or die(mysql_error());
 
/*echo "<script>window.alert('News Added Successfully') </script>";*/

}

?>

<!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=iso-8859-1" />

<title>Untitled Document</title>

<link href="KIMS-CSS.css" rel="stylesheet" type="text/css" />

<style type="text/css">

<!--

.style1 {font-size: 14px}

-->

</style>
 
<body>

<?php

$access = $_SESSION["access"];

if ($access != "authorized")

echo "<script>window.alert('You are not allowed to use this page'); window.location.replace('main_login.php'); </script>";
 
?>

<TABLE width="90%" border="0">

  <TR>

    <TD class="blue-17-bold"><DIV align="center" class="table-title-row style1">Add Subject </DIV></TD>

  </TR>

</TABLE>

<p>&nbsp;</p>

<form id="form1" name="form1" method="post" action="add_subject.php?action=add">

  <table width="356" border="1" align="center">
 
    <tr>

      <td>Subject Name</td>

      <td><input name="sub_name" type="text" id="descrip" onchange="return change(this)"/></td>

    </tr>

    <tr>

      <td colspan="2" align="center"><div>

        <label>

        <input name="Submit" type="submit" id="Submit" value="Add Subject" />

        </label>

      </div></td>

    </tr>

  </table>

</form>

<div>

  <div align="center" class="table-title-row style1">Show Subjects </div>

</div>

<p>&nbsp;</p>
 
<table width="716" border="1">

  <tr>

    <td width="105">Subject Code</td>

    <td width="110">Subject Name</td>
 
    <td width="66">Delete</td>

      </tr>

  <?php
 
$select=mysql_query("select * from subject") or die(mysql_error());
 
while($rs=mysql_fetch_array($select))

{

         $var=$rs[subject_code];

          $sub=$rs[Name];

?>

  <tr>

    <td><?php echo $rs['subject_code']; ?></td>

    <td><?php echo "<a href='add_question.php?code=$var&Name=$sub'> $rs[Name]</a><br/>"; ?></td>

    <td><a href="delete_subject.php?id=<?php echo $rs['subject_code']; ?>">Delete</a></td>

  </tr>

  <?php

  }

  ?>

</table>

</body>

</html>

and the add question page code is:

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<?php

session_start();

include("conn.php");

     connect();

$sub_code=$_GET['code'];

echo"$sub_code";
 
if($_GET['action']=="add")

{
 
//$sub_code=$_POST['sub_code'];

$question=$_POST['question'];

$weight=$_POST['weight'];
 
$result=mysql_query("insert into question values('','$question','$wieght','sub_code')") or die(mysql_error());
 
//*echo "<script>window.alert('News Added Successfully') </script>";*/

}

?>

<!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=iso-8859-1" />

<title>Untitled Document</title>

<link href="KIMS-CSS.css" rel="stylesheet" type="text/css" />

<style type="text/css">

<!--

.style1 {font-size: 14px}

-->

</style>
 
</head>

<body>

<?php

$access = $_SESSION["access"];

if ($access != "authorized")

echo "<script>window.alert('You are not allowed to use this page'); window.location.replace('main_login.php'); </script>";
 
?>

<table width="90%" border="0">

  <tr>

    <td class="blue-17-bold"><div align="center" class="table-title-row style1">Add Question </div></td>

  </tr>

</table>

<p>&nbsp;</p>

<form id="form1" name="form1" method="post" action="add_question.php?action=add">

  <table width="356" border="1" align="center">
 
    <tr>

      <td>Question</td>

      <td><input name="question" type="text" id="descrip" onchange="return change(this)"/></td>

    </tr>

<tr>

      <td>Weight</td>

      <td><input name="weight" type="text" id="descrip" onchange="return change(this)"/></td>

    </tr>

    <tr>

      <td colspan="2" align="center"><div>

        <label>

        <input name="Submit" type="submit" id="Submit" value="Add Subject" />

        </label>

      </div></td>

    </tr>

  </table>

</form>

<div>

  <div align="center" class="table-title-row style1">Show Subjects </div>

</div>

<p>&nbsp;</p>
 
<table width="716" border="1">

  <tr>

    <td width="105">Question Id    </td>

    <td width="110">Question</td>

<td width="110">Wieght</td>

<td width="110">Subject Code</td>
 
    <td width="66">Delete</td>

      </tr>

  <?php
 
$select=mysql_query("select * from question") or die(mysql_error());
 
while($rs=mysql_fetch_array($select))

{

         $var=$rs[question_id];

          $sub=$rs[question];

?>

  <tr>$sub_code=$_GET['code'];

    <td><?php echo $rs['question_id']; ?></td>

    <td><?php echo "<a href='add_answer.php?code=$var&Name=$sub'> $rs[questin]</a><br/>"; ?></td>

<td><?php echo $rs['weight']; ?></td>

<td><?php echo  $rs['sub_code']; ?></td>
 
    <td><a href="delete_subject.php?id=<?php echo $rs['question_id']; ?>">Delete</a></td>

  </tr>

  <?php

  }

  ?>

</table>

</body>

</html>

when i run this the following error occur

Cannot add or update a child row: a foreign key constraint fails (`kims`.`question`, CONSTRAINT `fk_question_subject` FOREIGN KEY (`sub_code`) REFERENCES `subject` (`subject_code`) ON DELETE NO ACTION ON UPDATE NO ACTION)

plz help thanks in advance....

Sep 28 '10 #1

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4882

JKing

1,206

Expert 1GB

You cannot insert data into a child table if the key does not exist in the parent table.

So in your case the related subject must exist before you insert a question for that subject.

Sep 28 '10 #2

semanticnotion

THANKS jking for your response,
i have already insert the subject before add the related question you can see it my data base table e.g 101 computer science. But the same error occur.

Sep 29 '10 #3

JKing

1,206

Expert 1GB

I think I may have spotted the source of your problem

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$result=mysql_query("insert into question values('','$question','$wieght','sub_code')") or die(mysql_error());

There is no $ in front of your sub_code variable so it is trying to insert the value "sub_code" and not the variable.

Sep 29 '10 #4

semanticnotion

I put $sub_code in query but still it not working. It take one question but when i insert another question it gives the above error.

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 $query="INSERT INTO  `kims`.`question` (`question` ,`weight` ,`sub_code`)VALUES ('$question',  '$weight',  '$sub_code')";
 
 

Sep 30 '10 #5

JKing

1,206

Expert 1GB

I think you need to possibly rework your form and rethink some of your logic here.

If you echo out your query before you run it, I think it will help illustrate your problem. You are rewriting your sub code variable to an empty string when you submit your add question form.

Sep 30 '10 #6

semanticnotion

yap i echo the query at first it take the value of $sub_code but when i insert another question the $sub_code is empty whats the reason of this i am not sure where i have a mistake.

Oct 4 '10 #7

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Cannot add or update a child row: a foreign key constraint fails (`kims`.`question`,

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