Passing value from SQL query to another SQL query in php

Question

I want to use a variable that comes from a table i MySQL and pass it to Another SQL-Query with PHP. Can´t get it to work and I can´t find out why.

Here is the code:

<html>
<head><title></title></head>
<body>
<div>

<?php

if (isset($_GET['read_blog_posts_scrolling']))
{

$result = mysql_query("SELECT blogpost.Blogpost_title, blog.Blogwriters_name, blogpost.Date 
FROM blog 
INNER JOIN blogpost ON blog.BlogID=blogpost.BlogID
WHERE blog.BlogID='$blogs_profile_id' // Here it is, it says undefined variable
ORDER BY blogpost.Date DESC")
or die(mysql_error());

while ($row = mysql_fetch_array($result)) {
			
			echo '<p>';
			echo "Titel: " . "<strong>" . $row['Blogpost_title'] . "</strong>" . " - Bloggare " . $row['Blogwriters_name'] . " " . $row['Date'] . '<br />';
			echo '<hr />';
			echo '</p>';

			}
}

?>

<?php

$result = mysql_query("SELECT BlogID, Blogwriters_name FROM blog")
or die(mysql_error());

while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) {

$blogs_profile_id = $row['BlogID']; // I want to pass this value to above and use it in the query

echo '<p>';

echo $row['Blogwriters_name'] . '<br />';

//When clicking in this link I want the query to execute and values in BlogID to be passed

echo '<a href="?read_blog_posts">Choose blogwriter</a>';

echo '</p>';

?>

</div>
</body>
</html>

it says the variable is undefined. How can I define it and pass the value when the a href-link is clicked?

devpro · Accepted Answer · 2016-01-17 08:58:04Z

Error is clear. Undefined variable:

You didn't defined this variable anywhere before select statement

$blogs_profile_id

I think you need to add this variable in query string and get from $_GET.

UPDATE 1:

You have following issues in your code.

Missing blog_profile_id in your query string.
Undefined variable means you are using a variable but didn't defined.
Using mysql_* extension its deprecated

Solution:

Replace this:

echo '<a href="?read_blog_posts">Choose blogwriter</a>';

With:

echo '<a href="?blog_id=$blogs_profile_id">Choose blogwriter</a>';

And than use that:

if (intval($_GET['blog_id']) > 0) 
{ 
      $blogs_profile_id = intval( $_GET['blog_id']);
      $result = mysql_query("SELECT blogpost.Blogpost_title, blog.Blogwriters_name, blogpost.Date FROM blog INNER JOIN blogpost ON blog.BlogID=blogpost.BlogID WHERE blog.BlogID=".$blogs_profile_id."  ORDER BY blogpost.Date DESC") 
or die(mysql_error());
.....

Thanga · Accepted Answer · 2016-01-18 06:22:09Z

0

Change the order of your queries. The second query code has to be coming first in order as below

<html>
<head><title></title></head>
<body>
<div>

<?php

$result = mysql_query("SELECT BlogID, Blogwriters_name FROM blog")
or die(mysql_error());

while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) {

$blogs_profile_id = $row['BlogID']; // I want to pass this value to above and use it in the query

echo '<p>';

echo $row['Blogwriters_name'] . '<br />';

//When clicking in this link I want the query to execute and values in BlogID to be passed

echo '<a href="?read_blog_posts">Choose blogwriter</a>';

echo '</p>';

?>


<?php

if (isset($_GET['read_blog_posts_scrolling']))
{

$result = mysql_query("SELECT blogpost.Blogpost_title, blog.Blogwriters_name, blogpost.Date 
FROM blog 
INNER JOIN blogpost ON blog.BlogID=blogpost.BlogID
WHERE blog.BlogID='"+$blogs_profile_id+"' // Here it is, it says undefined variable
ORDER BY blogpost.Date DESC")
or die(mysql_error());

while ($row = mysql_fetch_array($result)) {
			
			echo '<p>';
			echo "Titel: " . "<strong>" . $row['Blogpost_title'] . "</strong>" . " - Bloggare " . $row['Blogwriters_name'] . " " . $row['Date'] . '<br />';
			echo '<hr />';
			echo '</p>';

			}
}

?>



</div>
</body>
</html>

edited Jan 18, 2016 at 6:22

answered Jan 17, 2016 at 8:51

Thanga

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1 Comment

patriic48 Over a year ago

Can you give me an example? Cut&Paste from above?

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