Question

我想从表格中选择公司ID，日期和数字，但此查询并未显示一些公司的0号码。

以下是查询：

SELECT c.name, date_format(e.created, '%y_%m') AS date, count(*) 
FROM company c
JOIN edited e
on c.id=e.company_id AND e.created >='2016-12-13 00:00:00' AND e.created <='2017-05-20 00:00:00'
GROUP BY c.id, date

有些像这样的结果4 16_12 2 4 17_01 4 4 17_04 2 4 17_05 2 没有17_03（三月）。怎么能用0？

显示17_03

Answer 1

如果您的联接不符合ON子句中的值，则不会返回元组，因此您不会计算行数。如果您有一组固定的公司和日期，则可以使用UNION语句手动设置值：

(SELECT 'company_name1', 'date1', COUNT(*)
FROM company c
JOIN edited e
on c.id=e.company_id AND e.created >='2016-12-13 00:00:00' AND e.created <='2017-05-20 00:00:00')
UNION

(SELECT 'company_name2', 'date2', COUNT(*)
FROM company c
JOIN edited e
on c.id=e.company_id AND e.created >='2016-12-13 00:00:00' AND e.created <='2017-05-20 00:00:00')

#and make this for companies that not will return zero at count
UNION
(SELECT c.name, date_format(e.created, '%y_%m') AS date, count(*) 
FROM company c
JOIN edited e
on c.id=e.company_id AND e.created >='2016-12-13 00:00:00' AND e.created <='2017-05-20 00:00:00'
GROUP BY c.id, date)

Answer 2

SELECT c.id
     , ym.y
     , ym.m
     , count(e.created) cnt
  FROM ( SELECT @startDate := date_add(@startDate, interval 1 month) date
              , year(@startDate) y
              , month(@startDate) m
           FROM HugeTable
             JOIN ( SELECT @startDate := '2016-11-01' 
                         , @endDate   := '2017-05-01'
                  ) months
           WHERE @startDate < @endDate
       ) ym
    LEFT JOIN edited e
      ON    year(e.created)  = ym.y
        AND month(e.created) = ym.m
    LEFT JOIN company c
      ON c.id = e.company_id
  GROUP BY ym.y
         , ym.m
         , c.id

HugeTable 可以是任何具有足够记录数量的表格，作为要显示的月数。

如何选择每个月，即使他们没有价值

2 个答案: