SQL 分组后只获取每组的一条数据

/****** object:  table [dbo].[temp]    script date: 2018-8-22 星期三 23:33:09 ******/
set ansi_nulls on
go
set quoted_identifier on
go
create table [dbo].[temp](
	[id] [nvarchar](36) null,
	[serialno] [nvarchar](36) null,
	[qty] [numeric](10, 1) null,
	[foreignid] [nvarchar](32) null,
	[flag] [bit] not null,
	[createdate] [datetime] not null
) on [primary]

go
insert [dbo].[temp] ([id], [serialno], [qty], [foreignid], [flag], [createdate]) values (n'6073188b18574593b847dd0cac936dd5', n'1bf1c0f4f5034b2588b1c2e2b4f80294', cast(10.0 as numeric(10, 1)), n'f6df43bdc3ef4eaeb8c0d98c9abea7eb', 0, cast(0x0000a944017bbfef as datetime))
go
insert [dbo].[temp] ([id], [serialno], [qty], [foreignid], [flag], [createdate]) values (n'6073188b18574593b847dd0cac936dd5', n'1bf1c0f4f5034b2588b1c2e2b4f80294', cast(10.0 as numeric(10, 1)), n'b01892f11a284eea990afe0a4e4398b4', 0, cast(0x0000a944017bdef9 as datetime))
go
insert [dbo].[temp] ([id], [serialno], [qty], [foreignid], [flag], [createdate]) values (n'136eba69477c41879e4d0cf9a791d460', n'e60cffd61c314d248403cfd08370ed8c', cast(10.0 as numeric(10, 1)), n'4ca2da2abf434910b5d3d6ed6c343637', 0, cast(0x0000a944017c3f82 as datetime))
go
insert [dbo].[temp] ([id], [serialno], [qty], [foreignid], [flag], [createdate]) values (n'136eba69477c41879e4d0cf9a791d460', n'e60cffd61c314d248403cfd08370ed8c', cast(10.0 as numeric(10, 1)), n'b6fa2439e5bb44c58cff03b2725558d8', 0, cast(0x0000a944017c5604 as datetime))
go
insert [dbo].[temp] ([id], [serialno], [qty], [foreignid], [flag], [createdate]) values (n'136eba69477c41879e4d0cf9a791d460', n'e60cffd61c314d248403cfd08370ed8c', cast(11.0 as numeric(10, 1)), n'c465a72d36b5450e9a53e565ed95012d', 1, cast(0x0000a944017b4ec2 as datetime))
go
insert [dbo].[temp] ([id], [serialno], [qty], [foreignid], [flag], [createdate]) values (n'136eba69477c41879e4d0cf9a791d460', n'e60cffd61c314d248403cfd08370ed8c', cast(20.0 as numeric(10, 1)), n'd68efcd219634579966801b036ca8e29', 1, cast(0x0000a944017c7370 as datetime))
go
insert [dbo].[temp] ([id], [serialno], [qty], [foreignid], [flag], [createdate]) values (n'6073188b18574593b847dd0cac936dd5', n'1bf1c0f4f5034b2588b1c2e2b4f80294', cast(8.0 as numeric(10, 1)), n'2178fc8b537e4841a505e5e5a960ed83', 1, cast(0x0000a944017c94cd as datetime))
go
insert [dbo].[temp] ([id], [serialno], [qty], [foreignid], [flag], [createdate]) values (n'6073188b18574593b847dd0cac936dd5', n'1bf1c0f4f5034b2588b1c2e2b4f80294', cast(22.0 as numeric(10, 1)), n'7306f311b69e425cba13991030d7a2d3', 1, cast(0x0000a944017cb571 as datetime))
go
select * from dbo.temp a
where a.foreignid in (
	select top 1 b.foreignid from dbo.temp b where b.id = a.id and b.serialno = a.serialno
	order by b.flag,b.createdate
)