Error using mySQL build in operators - php

Question

I am using the MySQL build-in operators to get a running total, the query works well when I run it in phpMyAdmin, but running it in php does not work, I just get the "Couldn't execute query" message.
My database connection works fine, thus can I do this in php or is there another way to get this to work?
Here is the script:
include("../../include/xxx.inc");
$cxn = mysqli_connect($host,$user,$password,$dbname);
$query = "SET #runtot:=0;
SELECT `q1`.`c`, (#runtot := #runtot + `q1`.`c`) AS rt
FROM (
SELECT SUM( `sr`.`sr_qty` * `st`.`st_ton` ) AS c, `sr`.`sr_no`
FROM `sr`
JOIN `st` ON `sr`.`st_code` = `st`.`st_code`
WHERE `sr`.`sr_date` BETWEEN '2015-01-15' AND '2015-02-15'
GROUP BY `sr`.`sr_no`
ORDER BY `sr`.`sr_no`) AS q1";
$result = mysqli_query($cxn,$query)
or die ("Couldn't execute query.");
while($row = mysqli_fetch_assoc($result))
{
extract($row);
echo "$rt Ton";

Answer 1

Try setting the variable inside the query, so you only have one statement:
SELECT `q1`.`c`, (#runtot := #runtot + `q1`.`c`) AS rt
FROM (
SELECT SUM( `sr`.`sr_qty` * `st`.`st_ton` ) AS c, `sr`.`sr_no`
FROM (SELECT #runtst := 0) vars cross join
`sr`
JOIN `st` ON `sr`.`st_code` = `st`.`st_code`
WHERE `sr`.`sr_date` BETWEEN '2015-01-15' AND '2015-02-15'
GROUP BY `sr`.`sr_no`
ORDER BY `sr`.`sr_no`) AS q1

Answer 2

I'm not completely sure, but i think it's all your `'s
i would do SELECT 'q2.c', (# an so on.
But again, i might be wrong, but it's something to try.

Answer 3

You can't run multiple queries with mysqli_query. You need to call it separately for each query:
$query1 = "SET #runtot:=0"
$query2 = "SELECT `q1`.`c`, (#runtot := #runtot + `q1`.`c`) AS rt
FROM (
SELECT SUM( `sr`.`sr_qty` * `st`.`st_ton` ) AS c, `sr`.`sr_no`
FROM `sr`
JOIN `st` ON `sr`.`st_code` = `st`.`st_code`
WHERE `sr`.`sr_date` BETWEEN '2015-01-15' AND '2015-02-15'
GROUP BY `sr`.`sr_no`
ORDER BY `sr`.`sr_no`) AS q1";
mysqli_query($query1);
$result = mysqli_query($query2);
You can also put variable initializations into a subquery:
$query = "SELECT `q1`.`c`, (#runtot := #runtot + `q1`.`c`) AS rt
FROM (
SELECT SUM( `sr`.`sr_qty` * `st`.`st_ton` ) AS c, `sr`.`sr_no`
FROM `sr`
JOIN `st` ON `sr`.`st_code` = `st`.`st_code`
WHERE `sr`.`sr_date` BETWEEN '2015-01-15' AND '2015-02-15'
GROUP BY `sr`.`sr_no`
ORDER BY `sr`.`sr_no`) AS q1
CROSS JOIN (SELECT #runtot := 0) AS init";
mysqli also has mysqli_multi_query, which allows running multiple queries, but I've seen too many people run into problems to recommend it. It's rarely needed, IMHO.