using mysqli_multi_query to set variables of data - php

Question

I have just started to convert to mysqli due to the added security benefits. The main reason for converting to mysqli was the mysqli_multi_query function though. I had several long, complicated query's with a lot of JOINS in and when I found out about this function I thought I could make it simpler by breaking everything down into separate queries.
However, I have been unable to get the query to work as I want it to and the PHP manual isn't helping me.
Here's what I have so far;
$qry = "SELECT T.T_ID, T.name, T.pic, T.timestamp AS T_ts,
(SELECT COUNT(*) FROM track_plays WHERE T_ID = T.T_ID) AS plays,
(SELECT COUNT(*) FROM track_downloads WHERE T.T_ID = T_ID) AS downloads
FROM tracks T WHERE ID = '$ID';
";
$qry .= "SELECT S_ID, status, timestamp AS S_ts FROM status WHERE ID = '$ID';";
$qry .= "SELECT G_ID, gig_name, date_time, lineup, price, ticket, venue, G_pic, timestamp AS G_ts FROM gigs WHERE ID = '$ID'";
// Execute multi query
if (mysqli_multi_query($con,$qry)){
do {
// Store first result set
if ($result=mysqli_store_result($con)){
while ($row=mysqli_fetch_array($result)){
print_r($row);
}
}
}
while (mysqli_next_result($con));
}
This works fine and the array is printed as expected. However, i want to set a lot of variables for use later on. I won't list all of the variables but I have a few like this;
$S_ID = htmlspecialchars($row['S_ID']);
$T_ID = htmlspecialchars($row['T_ID']);
$G_ID = htmlspecialchars($row['G_ID']);
The variables are retrieved but due to the loop nature of the function PHP errors are given as well saying the $S_ID or $G_ID are undefined. $T_ID does not get an undefined error as it is the first query as is not looped over.
If you need any more information or I have not explained well enough just ask!

Answer 1

A while back ago i have had the same issues, and also for the same reason i have migrated from mysql to mysqli.
Sadly, it wasnt the best sollution for many cases, as i have realized on the way.
While implementing stuff with mysqli and multi query i still have had some issues that i had with mysql.
The solution i recommend, is to use views on your complicated querys.
it makes your coding and querys far less complicated.
I know it is not the answer you have been looking for, but give it a thought.

Answer 2

So far, every time I use a mysqli_multi_query, my do-while condition is:
while(mysqli_more_results($connection) && mysqli_next_result($connection));
You may like to replace your while statement and see if that helps.
If not, are you differentiating between each subsequent query when you are assigning these $S_ID, $G_ID variables? Are you inadvertently overwriting a variable with an empty $row[] value?
I also didn't see mysqli_free_result($result) in your code.
I'll even offer some error checking as a garnish.
preg_match_all("/(?:SELECT\s(.*?),\s.*?(?:;|$))/",$qry,$first_columnname);
if (mysqli_multi_query($con,$qry)){
do {
if ($result=mysqli_store_result($con)){
$query_identifier=array_shift($first_columnname[1]);
while ($row=mysqli_fetch_array($result)){
if($query_identifier)=="T.T_ID"){
//do something...
}elseif($query_identifier)=="S_ID"){
//do something...
}elseif($query_identifier)=="G_ID"){
//do something...
}
}
mysqli_free_result($result);
}
}
while(mysqli_more_results($con) && mysqli_next_result($con));
}
if($error_mess=mysqli_error($con)){echo "Error = $error_mess";}
Let me know if any of these small changes do the trick.