如何用遞歸解決連續序列中的間隙？

Question

X Y 
------- 
A 1 
B 5 
C 9 

我有一個像上面的數據的結果集，並希望實現前面的記錄X的值的記錄對應於Y中的差距，這基本上是類似於下面的數據的東西。有什麼不同的方式來實現這一點？

X Y 
------- 
A 1 
A 2 
A 3 
A 4 
B 5 
B 6 
B 7 
B 8 
C 9 

Answer 1

declare @tbl table 
(
    X char, 
    Y int 
) 

insert into @tbl select 'A', 1 
insert into @tbl select 'B', 5 
insert into @tbl select 'C', 9 

-- Query 1 : recursive CTE 
; with 
cte as 
(
    select rn = ROW_NUMBER() over (order by Y), X, Y 
    from @tbl 
), 
rcte as 
(
    select rn, X, Y 
    from cte 
    where rn = 1 

    union all 

    select rn = case when r.Y + 1 < c.Y then r.rn else c.rn end, 
     X = case when r.Y + 1 < c.Y then r.X else c.X end, 
     Y = case when r.Y + 1 < c.Y then r.Y + 1 else c.Y end 
    from rcte r 
     inner join cte c on r.rn = c.rn - 1 
) 
select * 
from rcte 

-- Query 2 : tally table method. Required SQL Server 2012+ 

; with tally as 
(
    select n = 1 
    union all 
    select n = n + 1 
    from tally 
    where n <= 100 
), 
cte as 
( select *, next_Y = isnull(LEAD(Y) OVER (ORDER BY Y), Y + 1) 
    from @tbl t 
) 
select c.X, n.n as Y 
from cte c 
    cross join tally n 
where n.n >= c.Y 
and n.n < c.next_Y 

Answer 2

試試這個簡單的查詢，（假設@tbl是你的表/結果集）

WITH cte_test 
AS 
(
    SELECT t.X,t.Y,isnull((SELECT min(t1.Y) FROM @tbl t1 WHERE t1.X > t.X),t.Y) AS maxval FROM @tbl t 
    UNION ALL 
    SELECT t.X,c.Y+1,c.maxval FROM cte_test c 
    INNER JOIN @tbl t ON c.X = t.X 
    WHERE c.Y+1 < c.maxval 
) 
SELECT X,Y FROM cte_test ORDER BY 1,2