SQL Query giving an error of Unknown Column - mysql

Question

I am creating an application in PHP of Power Meter Analysis. I have following table structure:
table: 'feeds'
| feed_id | device_no | current1 | voltage1 | power_factor_1 | vc1 | ic1 | date_added
-------------------------------------------------------------------------------------
| 36752 | 2 | 36.048 | 196.01 | 0.9 | 1 | 1 | 2014-06-23 14:14:44
| 36753 | 2 | 35.963 | 195.59 | 0.9 | 1 | 1 | 2014-06-23 14:15:34
and so on.
table: 'machine'
| machine_id | machine_phone | machine_name | company_id |
----------------------------------------------------------
| 1 | 2 | ABC Machine | 1 |
| 2 | 093 | DEF Machine | 1 |
I need records on hourly basis and I have written the following query for this purpose:
$sql = "
SELECT
SUM(t.power1) AS 'power1'
, HOUR(t.date) AS 'pulse_hour'
FROM (
SELECT
IF(#diff = 0, 0, (((f.voltage1*f.vc1)*(f.current1*f.ic1)*(f.power_factor_1))/1000) * (#diff/3600)) AS 'power1'
, IF(#diff = 0,0, TIME_TO_SEC(f.date_added) - #diff) AS 'deltaT'
, #diff := TIME_TO_SEC(f.date_added)
, f.date_added AS 'date'
FROM
feeds f,
(SELECT #diff := 0) AS X
left join
machine m
on
f.device_no = m.machine_phone
left join
company c
on
c.company_id = m.company_id
";
$sql .= $params['machine_id'] ? " where f.device_no = '".$params['machine_id']."'" : " where f.device_no > 0";
$sql .= $params['machine_pulse_datetime_from'] ? " and f.date_added >= '".$params['machine_pulse_datetime_from']."'" : "";
$sql .= $params['machine_pulse_datetime_to'] ? " and f.date_added <= '".$params['machine_pulse_datetime_to']."'" : "";
$sql .= $params['company_id'] ? " and c.company_id = '".$params['company_id']."'" : "";
$sql .= "
ORDER BY
f.date_added ASC
) t
GROUP BY HOUR(t.date)
ORDER BY HOUR(t.date) ASC
";
The query is running OK if I remove the following part from the query:
left join
machine m
on
f.device_no = m.machine_phone
left join
company c
on
c.company_id = m.company_id
But with this part It is giving me following error:
Error Code : 1054
Unknown column 'f.device_no' in 'on clause'
can you please help me to sort this out... I have spent an hour with this query :(

Answer 1

This is your join:
FROM feeds f,
(SELECT #diff := 0) AS X left join
machine m
on f.device_no = m.machine_phone left join
company c
on c.company_id = m.company_id
The problem is that you are mixing explicit and implicit joins. You can fix this by replacing the comma with cross join:
FROM feeds f cross join
(SELECT #diff := 0) AS X left join
machine m
on f.device_no = m.machine_phone left join
company c
on c.company_id = m.company_id
The issue, which is buried deep in the documentation for select, is that , is a lot like a cross join with the exception of scoping rules -- that is, when the table aliases are recognized. With a comma, the table aliases are not recognized as you expect. They are with a cross join.
Here is the reference:
INNER [CROSS] JOIN and , (comma) are semantically equivalent in the
absence of a join condition: both produce a Cartesian product between
the specified tables (that is, each and every row in the first table
is joined to each and every row in the second table).
However, the precedence of the comma operator is less than of INNER
JOIN, CROSS JOIN, LEFT JOIN, and so on. If you mix comma joins
with the other join types when there is a join condition, an error of
the form Unknown column 'col_name' in 'on clause' may occur.
Information about dealing with this problem is given later in this
section.