我有一个类似于以下内容的SQL表:
ID, Date, D1, D2, D3
1 1/1/13 0 X A
2 1/2/13
3 1/3/13 1
4 1/4/13 B
5 1/5/13
我需要更新到以下内容:
ID, Date, D1, D2, D3
1 1/1/13 0 X A
2 1/2/13 0 X A
3 1/3/13 1 X A
4 1/4/13 1 X B
5 1/5/13 1 X B
基本上用前面的值填充所有空值。这只会执行一次。循环是最好的选择吗?或者是否有更有效的东西?
答案 0 :(得分:5)
假设您正在使用SQL-Server,您可以使用此common-table-expression:
WITH cte
AS (SELECT T1.id,
T1.date,
d1 = COALESCE(T1.d1, (SELECT TOP 1 d1
FROM dbo.tablename T2
WHERE T2.id < T1.id
AND d1 IS NOT NULL
ORDER BY id DESC)),
d2 = COALESCE(T1.d2, (SELECT TOP 1 d2
FROM dbo.tablename T2
WHERE T2.id < T1.id
AND d2 IS NOT NULL
ORDER BY id DESC)),
d3 = COALESCE(T1.d3, (SELECT TOP 1 d3
FROM dbo.tablename T2
WHERE T2.id < T1.id
AND d3 IS NOT NULL
ORDER BY id DESC))
FROM dbo.tablename T1)
UPDATE T
SET T.d1 = C.d1,
T.d2 = C.d2,
T.d3 = C.d3
FROM dbo.tablename T
INNER JOIN cte C
ON T.id = C.id
WHERE T.d1 IS NULL
OR T.d2 IS NULL
OR T.d3 IS NULL
修改由于您在评论中提到''
而不是null
,因此这是一个支持这两者的修改版本:
WITH cte AS
(SELECT T1.id,
T1.date,
d1 = CASE WHEN COALESCE(T1.d1, '') <> '' THEN d1
ELSE(SELECT TOP 1 d1
FROM dbo.tablename T2
WHERE T2.id < T1.id
AND COALESCE(T2.d1, '') <> ''
ORDER BY T2.id DESC) END,
d2 = CASE WHEN COALESCE(T1.d2, '') <> '' THEN d2
ELSE(SELECT TOP 1 d2
FROM dbo.tablename T2
WHERE T2.id < T1.id
AND COALESCE(T2.d2, '') <> ''
ORDER BY T2.id DESC) END,
d3 = CASE WHEN COALESCE(T1.d3, '') <> '' THEN d3
ELSE(SELECT TOP 1 d3
FROM dbo.tablename T2
WHERE T2.id < T1.id
AND COALESCE(T2.d3, '') <> ''
ORDER BY T2.id DESC) END
FROM dbo.tablename T1)
UPDATE T
SET T.d1 = C.d1,
T.d2 = C.d2,
T.d3 = C.d3
FROM dbo.tablename T
INNER JOIN cte C
ON T.id = C.id
WHERE COALESCE(T.d1, '') = ''
OR COALESCE(T.d2, '') = ''
OR COALESCE(T.d3, '') = ''
答案 1 :(得分:1)
假设我们使用ID
列来确定顺序,您可以在没有循环的情况下执行此操作。
你想要这样做是另一回事 - 它看起来不漂亮:
declare @t table (ID int, Date date, D1 int, D2 char(1), D3 char(1))
insert into @t(ID, Date, D1, D2, D3) values
(1,'20130101',0,'X','A'),
(2,'20130201',null,null,null),
(3,'20130301',1,null,null),
(4,'20130401',null,null,'B'),
(5,'20130501',null,null,null)
update a
set
a.D1 = COALESCE(a.D1,d1.D1),
a.D2 = COALESCE(a.D2,d2.D2),
a.D3 = COALESCE(a.D3,d3.D3)
from
@t a
left join
@t D1
on
D1.ID < a.ID and
D1.D1 IS NOT NULL
left join
@t D1_anti
on
D1_anti.ID < a.ID and
D1_anti.D1 is not null and
D1_anti.ID > D1.ID
left join
@t D2
on
D2.ID < a.ID and
D2.D2 IS NOT NULL
left join
@t D2_anti
on
D2_anti.ID < a.ID and
D2_anti.D2 is not null and
D2_anti.ID > D2.ID
left join
@t D3
on
D3.ID < a.ID and
D3.D3 IS NOT NULL
left join
@t D3_anti
on
D3_anti.ID < a.ID and
D3_anti.D3 is not null and
D3_anti.ID > D3.ID
where
D1_anti.ID is null and
D2_anti.ID is null and
D3_anti.ID is null
select * from @t
基本上,我们执行连接以尝试查找可能适用的早期行,然后执行_anti
连接以确保每个找到的前一行是最新的存在行。