How to get a count even if there are no results corresponding mysql?

Question

I am formalating a query to give the number of reports submitted over the last year ordered by date. I get the current year and month with php:

$year = date('Y') - 1;
$month = date('m');

and execute the following query: SQL:

SELECT month(date_lm) AS `month` ,
count(*) AS `count`
FROM `reports` 
WHERE (status = 'submitted') 
AND (date_lm > 2012-08) 
GROUP BY month(date_lm) 
ORDER BY month(date_lm) ASC

And because there has only been 1 submitted in the last year it gives me only 1 result...

| month  |  count  |
|   7    |    1    |

But I would like the result set to show:

| month  |  count  |
|   9    |    0    |
|   10   |    0    |
|   11   |    0    |
|   12   |    0    |
|   1    |    0    |
|   2    |    0    |
|   3    |    0    |
|   4    |    0    |
|   5    |    0    |
|   6    |    0    |
|   7    |    1    |
|   8    |    0    |

Is that possible?

Solution 1

You should LEFT JOIN this table with 1..12 table. Something like this:

SELECT  Months.id AS `month` ,
COUNT(`reports`.date_lm) AS `count`
FROM 
(
  SELECT 1 as ID UNION SELECT 2 as ID UNION  SELECT 3 as ID UNION SELECT 4 as ID 
  UNION  
  SELECT 5 as ID UNION SELECT 6 as ID UNION SELECT 7 as ID UNION SELECT 8 as ID 
  UNION  
  SELECT 9 as ID UNION SELECT 10 as ID UNION SELECT 11 as ID UNION SELECT 12 as ID
) as Months
LEFT JOIN `reports` on Months.id=month(`reports`.date_lm)
                       AND 
                       (status = 'submitted') 
                       AND (date_lm > 2012-08)
GROUP BY Months.id 
ORDER BY Months.id ASC

SQL Fiddle demo

Solution 2

count(col_name) AS count will give you count 0

For reference you can visit http://www.mysqlperformanceblog.com/2007/04/10/count-vs-countcol/

Solution 3

In order to do this, you could create a 'month' table and then use a left outer join between that table and the reports table.

I've never used mysql so apologies if the syntax is slightly off, but this would be the query:

SELECT months.monthNumber,
    count(reports.id) AS `count`
FROM `months` left outer join `reports` on months.monthNumber = month(reports.date_lm) 
WHERE (status = 'submitted') 
AND (date_lm > 2012-08) 
GROUP BY monthNumber
ORDER BY monthNumber ASC

Importantly, the count should be of a column in the reports table, not the months table, or else you would never get a zero.

Comments

[tread]

Hi thanks, This seems legit but I get a FUNCTION reports.month does not exist.Check with function name parsing and resolution.

[valex]

@StevieG: try fixed query

[tread]

It's working now, but the output is still not outputting months 9 through to 8. So only when a row that meets the conditions it is added. So there are none with a 0 count.

[tread]

thanks appreciate your time man. Is there a way to make months of previous year ie. 09-2012, 10-2012, appear before the others instead of in ascending order?

[carinlynchin]

I've tried so many ways to do this but I ended up with the error: ERROR 1267 (HY000): Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='

[mickmackusa]

"hope this helps" answers do a poor job of educating the OP and thousands of future researchers. Please always explain how your snippet works and why it is a good idea.