Mysql sum of records by month for the last 12 months

问题

Hello I'm using this sql query to get the last 12 month records based on month for chart representation:

SELECT DATE_FORMAT(drives.timestamp, "%b") AS Month,
                         DATE_FORMAT(drives.timestamp, "%d-%m-%Y %H:%i:%s") AS Exact_date,
                         drives.departure,
                         drives.destination,
                         drives.route,
                         CONCAT(drivers.name, " ", drivers.surname) as driver,
                         drivers.id as driver_id
                         FROM drives, drivers WHERE drives.driver = drivers.id 
                         AND drives.timestamp > DATE_SUB(now(), INTERVAL 12 MONTH) ORDER BY drives.timestamp Asc

however if there are no records for a month it is not included in the result set as expected, and I'm doing a lot of calculations with php to accomplish what I want.

My question is this: Is there a way to retrieve a simple result set with the sum of drives of each month for the last 12 months AND if there are 0 drives for a month it must be also included-shown in the result set.

回答1:

You need to do an outer join with a table that contains a row for each month. Assuming you don't have such a table, you can create it on the fly with a hard-coded UNION query:

SELECT * FROM
    (SELECT DATE_FORMAT(now(), "%b") as Month
     UNION
     SELECT DATE_FORMAT(now() - INTERVAL 1 MONTH), "%b")
     UNION
     SELECT DATE_FORMAT(now() - INTERVAL 2 MONTH), "%b")
     UNION
     ...
     SELECT DATE_FORMAT(now() - INTERVAL 11 MONTH), "%b")) AS Months
LEFT JOIN (SELECT DATE_FORMAT(drives.timestamp, "%b") AS Month,
                 drives.timestamp,
                 DATE_FORMAT(drives.timestamp, "%d-%m-%Y %H:%i:%s") AS Exact_date,
                 drives.departure,
                 drives.destination,
                 drives.route,
                 CONCAT(drivers.name, " ", drivers.surname) as driver,
                 drivers.id as driver_id
                 FROM drives, drivers WHERE drives.driver = drivers.id 
                 AND drives.timestamp > DATE_SUB(now(), INTERVAL 12 MONTH)) data
ON Months.Month = data.Month
ORDER BY data.timestamp

Any months with no records will have one row with NULL in the data columns.

来源：https://stackoverflow.com/questions/19757458/mysql-sum-of-records-by-month-for-the-last-12-months

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