group by month and year, count from another table

问题

im trying to get my query to group rows by month and year from the assignments table, and count the number of rows that has a certain value from the leads table. they are linked together as the assignments table has an id_lead field, which is the id of the row in the leads table.

d_new would be a count of the assignments for leads for the month whose website is newsite.com d_subprime would be a count of the assignments for leads for the month whose website is not newsite.com

here are the tables being used:

`leads`
id (int)
website (varchar)

`assignments`
id_lead (int)
date_assigned (int)

heres my query which is not working:

SELECT 
  MONTHNAME(FROM_UNIXTIME(a.date_assigned)) as d_month, 
  YEAR(FROM_UNIXTIME(a.date_assigned)) as d_year, 
  (select COUNT(*) from leads where website='newsite.com' ) as d_new,
  (select COUNT(*) from leads where website!='newsite.com') as d_subprime
FROM assignments as a
left join leads as l on (l.id = a.id_lead)
where id_dealership='$id_dealership2'
GROUP BY 
  d_month, 
  d_year
ORDER BY
    d_year asc,
    MONTH(FROM_UNIXTIME(a.date_assigned)) asc

$id_dealership is a variable containing a id of the dealership im trying to view the count for.

any help would be greatly appreciated.

回答1:

You can sort of truncate your timestamps to months and use the obtained values for grouping, then derive the necessary date parts from them:

SELECT
  YEAR(d_yearmonth) AS d_year,
  MONTHNAME(d_yearmonth) AS d_month,
  …
FROM (
  SELECT
    LAST_DAY(FROM_UNIXTIME(a.date_assigned)) as d_yearmonth,
    …
  FROM assignments AS a
    LEFT JOIN leads AS l ON (l.id = a.id_lead)
  WHERE id_dealership = '$id_dealership2'
  GROUP BY
    d_yearmonth
) AS s
ORDER BY
  d_year            ASC,
  MONTH(d_yearmonth) ASC

Well, LAST_DAY() doesn't really truncate a timestamp, but it does turn all the values belonging to the same month into the same value, which is basically what we need.

And I guess the counts should be related to the rows you are actually selecting, which is not what your subqueries are. Something like this might do:

…
COUNT(d.website = 'newsite.com' OR NULL) AS d_new,
/* or: COUNT(d.website) - COUNT(NULLIF(d.website, 'newsite.com')) AS d_new */
COUNT(NULLIF(d.website, 'newsite.com'))  AS d_subprime
…

Here's the entire query with all the modifications mentioned:

SELECT
  YEAR(d_yearmonth) AS d_year,
  MONTHNAME(d_yearmonth) AS d_month,
  d_new,
  d_subprime
FROM (
  SELECT
    LAST_DAY(FROM_UNIXTIME(a.date_assigned)) as d_yearmonth,
    COUNT(d.website = 'newsite.com' OR NULL) AS d_new,
    COUNT(NULLIF(d.website, 'newsite.com'))  AS d_subprime
  FROM assignments AS a
    LEFT JOIN leads AS l ON (l.id = a.id_lead)
  WHERE id_dealership = '$id_dealership2'
  GROUP BY
    d_yearmonth
) AS s
ORDER BY
  d_year            ASC,
  MONTH(d_yearmonth) ASC

回答2:

This should do the trick:

SELECT
YEAR(FROM_UNIXTIME(a.date_assigned)) as d_year, 
MONTHNAME(FROM_UNIXTIME(a.date_assigned)) as d_month,
l.website,
COUNT(*)
FROM
assignments AS a
INNER JOIN leads AS l on (l.id = a.id_lead) /*are you sure, that you need a LEFT JOIN?*/
WHERE id_dealership='$id_dealership2'
GROUP BY
d_year, d_month, website
/*an ORDER BY is not necessary, MySQL does that automatically when grouping*/

If you really need a LEFT JOIN, be aware that COUNT() ignores NULL values. If you want to count those as well (which I can't imagine to make sense) write it like this:

SELECT
YEAR(FROM_UNIXTIME(a.date_assigned)) as d_year, 
MONTHNAME(FROM_UNIXTIME(a.date_assigned)) as d_month,
l.website,
COUNT(COALESCE(l.id, 1))
FROM
assignments AS a
LEFT JOIN leads AS l on (l.id = a.id_lead)
WHERE id_dealership='$id_dealership2'
GROUP BY
d_year, d_month, website

回答3:

Start with

SELECT 
  MONTHNAME(FROM_UNIXTIME(a.date_assigned)) as d_month, 
  YEAR(FROM_UNIXTIME(a.date_assigned)) as d_year, 
  SUM(IF(l.website='newsite.com',1,0) AS d_new,
  SUM(IF(l.website IS NOT NULL AND l.website!='newsite.com',1,0) AS d_subprime
FROM assignments AS a
LEFT JOIN leads AS l ON l.id = a.id_lead
WHERE id_dealership='$id_dealership2'
GROUP BY 
  d_month, 
  d_year
ORDER BY
    d_year asc,
    MONTH(FROM_UNIXTIME(a.date_assigned)) asc

and work from here: The field id_dealership is neither in leads nor in assignments, so you need more work.

If you edit your question to account for id_dealership we might be able to help you further.

来源：https://stackoverflow.com/questions/9699533/group-by-month-and-year-count-from-another-table