SQL Server中公用表表达式（CTE）递归的生成帮助数据

可以直接让CTE参数逻辑运算，也可以生成临时表，达到多次重用的目的，这样感觉是不是也很清爽？

1，生成连续数字（当然数字的起始值，间隔值都可以自定义）

--生成连续数字
;with GenerateHelpData
as
(
    select 0 as id
    union all
    select id+1 from GenerateHelpData where id<2047
)
select id from GenerateHelpData option (maxrecursion 2047);

2，CTE递归生成连续日期

--生成连续日期
;with GenerateHelpData
as
(
    select cast(‘2016-10-01‘ as date) as [Date]
    union all
    select DATEADD(D,1,[Date]) from GenerateHelpData where [Date]<‘2017-01-01‘
)
select [Date] from GenerateHelpData;

3，生成连续间隔的时间点

　　有时候一些统计需要按照一个小时或者半个小时之类的时间间隔做组合，比如统计某天内没半个小时的小时数据等等

--生成连续间隔的时间点
;with GenerateHelpData
as
(
    select 1 as id, cast(‘00:00:00‘ as time(0)) as timeSection
    union all
    select id+1 as id,  cast(dateadd(mi,30,timeSection) as time(0)) as timeSection 
     from GenerateHelpData  where id<49
)
select * from GenerateHelpData

当然这里就可以非常灵活了，更骚一点的变形

--更骚一点的变形
;with GenerateHelpData
as
(
    select 1 as id, cast(‘00:00:00‘ as time(0)) as timeSection
    union all
    select id+1 as id,  cast(dateadd(mi,30,timeSection) as time(0)) as timeSection 
     from GenerateHelpData  where id<49
)
select 
A.timeSection as timeSectionFrom,
B.timeSection as timeSectionTo,
cast(A.timeSection as varchar(10))+‘~‘+cast(B.timeSection as varchar(10)) as timeSection
from GenerateHelpData  A inner join GenerateHelpData B on A.id= B.id-1

　　4，生成连续季度的最后一天

DECLARE 
@begin_date date = ‘2014-12-31‘,
@end_date date = ‘2016-12-31‘
;with GenerateHelpData as
(
    select 
        CAST(    CASE 
                    WHEN RIGHT(@begin_date,5)=‘12-30‘ 
                THEN DATEADD(DAY,1,@begin_date) 
                    ELSE @begin_date 
                END AS    DATE)
        AS EndingDate
    UNION ALL
    SELECT     
        CASE WHEN RIGHT(DATEADD(QQ,1,EndingDate),5)=‘12-30‘ 
        THEN  DATEADD(DAY,1,DATEADD(QQ,1,EndingDate)) 
        ELSE DATEADD(QQ,1,EndingDate)
        END AS EndingDate
    from GenerateHelpData where EndingDate< @end_date
)
select * from GenerateHelpData

通过变形可以生成两个日期间隔之间的的数据

DECLARE 
@begin_date date = ‘2014-12-31‘,
@end_date date = ‘2016-12-31‘
;with GenerateHelpData as
(
    select 1 as id ,
        CAST(    CASE 
                    WHEN RIGHT(@begin_date,5)=‘12-30‘ 
                THEN DATEADD(DAY,1,@begin_date) 
                    ELSE @begin_date 
                END AS    DATE)
        AS EndingDate
    UNION ALL
    SELECT     id+1 as id,
        CASE WHEN RIGHT(DATEADD(QQ,1,EndingDate),5)=‘12-30‘ 
        THEN  DATEADD(DAY,1,DATEADD(QQ,1,EndingDate)) 
        ELSE DATEADD(QQ,1,EndingDate)
        END AS EndingDate
    from GenerateHelpData where EndingDate< @end_date
)
select 
A.EndingDate as DateFrom,
B.EndingDate as DateTo,
cast(A.EndingDate as varchar(10))+‘~‘+cast(B.EndingDate as varchar(10)) as timeSection
from GenerateHelpData  A inner join GenerateHelpData B on A.id= B.id-1

需要注意的是，CTE递归的默认次数是100，如果不指定递归次数（option (maxrecursion N);），超出默认最大递归次数之后会报错。

 　总结：本文演示了几种常用的根据CTE递归生成帮助数据的情况，如果需要帮助数据，可以根据CTE的递归特性做灵活处理。

SQL Server中公用表表达式（CTE）递归的生成帮助数据

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