我考虑过使用递归 CTE，但是，据我所知，在 SQL Server 中无法UNION用于连接锚成员和递归 CTE 的递归成员（我认为在 PostgreSQL 中可以做到），所以不可能消除重复。
declare @i int
with cte as (
select
GroupID,
row_number() over(order by Company) as rn
from Table1
)
update cte set GroupID = rn
select @i = @@rowcount
-- while some rows updated
while @i > 0
begin
update T1 set
GroupID = T2.GroupID
from Table1 as T1
inner join (
select T2.Company, min(T2.GroupID) as GroupID
from Table1 as T2
group by T2.Company
) as T2 on T2.Company = T1.Company
where T1.GroupID > T2.GroupID
select @i = @@rowcount
update T1 set
GroupID = T2.GroupID
from Table1 as T1
inner join (
select T2.Publisher, min(T2.GroupID) as GroupID
from Table1 as T2
group by T2.Publisher
) as T2 on T2.Publisher = T1.Publisher
where T1.GroupID > T2.GroupID
-- will be > 0 if any rows updated
select @i = @i + @@rowcount
end
;with cte as (
select
GroupID,
dense_rank() over(order by GroupID) as rn
from Table1
)
update cte set GroupID = rn
sql fiddle demo
我还尝试了广度优先搜索算法。我认为它可以更快（在复杂性方面更好），所以我将在这里提供一个解决方案。不过，我发现它并不比 SQL 方法快：
declare @Company nvarchar(2), @Publisher nvarchar(2), @GroupID int
declare @Queue table (
Company nvarchar(2), Publisher nvarchar(2), ID int identity(1, 1),
primary key(Company, Publisher)
)
select @GroupID = 0
while 1 = 1
begin
select top 1 @Company = Company, @Publisher = Publisher
from Table1
where GroupID is null
if @@rowcount = 0 break
select @GroupID = @GroupID + 1
insert into @Queue(Company, Publisher)
select @Company, @Publisher
while 1 = 1
begin
select top 1 @Company = Company, @Publisher = Publisher
from @Queue
order by ID asc
if @@rowcount = 0 break
update Table1 set
GroupID = @GroupID
where Company = @Company and Publisher = @Publisher
delete from @Queue where Company = @Company and Publisher = @Publisher
;with cte as (
select Company, Publisher from Table1 where Company = @Company and GroupID is null
union all
select Company, Publisher from Table1 where Publisher = @Publisher and GroupID is null
)
insert into @Queue(Company, Publisher)
select distinct c.Company, c.Publisher
from cte as c
where not exists (select * from @Queue as q where q.Company = c.Company and q.Publisher = c.Publisher)
end
end
sql fiddle demo
我已经测试了我的版本和 Gordon Linoff 的版本来检查它的性能。看起来 CTE 更糟糕，我等不及它在 1000 多行上完成了。
这是带有随机数据的sql fiddle 演示。我的结果是：
128 行：
我的 RBAR 解决方案：190ms
我的 SQL 解决方案：27ms
Gordon Linoff 的解决方案：958ms
256 行：
我的 RBAR 解决方案：560ms
我的 SQL 解决方案：1226ms
Gordon Linoff 的解决方案：45371ms
这是随机数据，所以结果可能不是很一致。我认为时间可以通过索引来改变，但不认为它可以改变整个画面。
旧版本 - 使用临时表，只计算 GroupID 而不接触初始表：
declare @i int
-- creating table to gather all possible GroupID for each row
create table #Temp
(
Company varchar(1), Publisher varchar(1), GroupID varchar(1),
primary key (Company, Publisher, GroupID)
)
-- initializing it with data
insert into #Temp (Company, Publisher, GroupID)
select Company, Publisher, Company
from Table1
select @i = @@rowcount
-- while some rows inserted into #Temp
while @i > 0
begin
-- expand #Temp in both directions
;with cte as (
select
T2.Company, T1.Publisher,
T1.GroupID as GroupID1, T2.GroupID as GroupID2
from #Temp as T1
inner join #Temp as T2 on T2.Company = T1.Company
union
select
T1.Company, T2.Publisher,
T1.GroupID as GroupID1, T2.GroupID as GroupID2
from #Temp as T1
inner join #Temp as T2 on T2.Publisher = T1.Publisher
), cte2 as (
select
Company, Publisher,
case when GroupID1 < GroupID2 then GroupID1 else GroupID2 end as GroupID
from cte
)
insert into #Temp
select Company, Publisher, GroupID
from cte2
-- don't insert duplicates
except
select Company, Publisher, GroupID
from #Temp
-- will be > 0 if any row inserted
select @i = @@rowcount
end
select
Company, Publisher,
dense_rank() over(order by min(GroupID)) as GroupID
from #Temp
group by Company, Publisher
=> sql 小提琴示例