TSQL - 返回开始日期和结束日期之间每个月的记录，即使该月没有可用数据

Question

我目前的SELECT查询结果如下

SELECT Category, MonthYear, Percentage 
FROM #Result

@StartDate 为 2018-12-01，@EndDate 为 2019-05-01

Category  | MonthYear  | Percentage
----------+------------+------------    
Category1 | 2018-12-01 | 80 
Category1 | 2019-01-01 | 70
Category1 | 2019-02-01 | 75
Category1 | 2019-03-01 | 60
Category1 | 2019-04-01 | 45
Category1 | 2019-05-01 | 29
Category2 | 2019-03-01 | 78
Category2 | 2019-04-01 | 95
Category2 | 2019-05-01 | 98

但我希望我的结果对于每个 Categories 都有介于 @StartDate 和 @EndDate 之间的所有月份，如果该类别不存在数据，则百分比值为零。

Category  | MonthYear  | Percentage
----------+------------+------------    
Category1 | 2018-12-01 | 80 
Category1 | 2019-01-01 | 70
Category1 | 2019-02-01 | 75
Category1 | 2019-03-01 | 60
Category1 | 2019-04-01 | 45
Category1 | 2019-05-01 | 29
Category2 | 2018-12-01 | 0
Category2 | 2019-01-01 | 0
Category2 | 2019-02-01 | 0
Category2 | 2019-03-01 | 78
Category2 | 2019-04-01 | 95
Category2 | 2019-05-01 | 98

Answer 1

您可以使用递归 CTE 来生成日期。然后使用cross join 和left join 来引入数据。所以：

with dates as (
      select min(monthyear) as yyyymm, max(monthyear) as max_yyyymm
      from t
      union all
      select dateadd(month, 1, yyyymm), max_yyyymm
      from dates
      where yyyymm < max_yyyymm
    )
select c.category, d.yyyymm, coalesce(t.percentage, 0) as percentage
from (select distinct category from t) c cross join
     dates d left join
     t
     on t.category = c.category and t.monthyear = d.yyyymm
order by c.category, d.yyyymm;