bigtable unpivot [stackexchange 175000], Sql Server

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CREATE TABLE dbo.bigtable
(UpdateDate datetime      not null
,PK         varchar(12)   not null
,col1       varchar(100)      null
,col2       int               null
,col3       varchar(20)       null
,col4       datetime          null
,col5       char(20)          null
,PRIMARY KEY (PK)
);

CREATE TABLE dbo.bigtable_archive
(UpdateDate datetime      not null
,PK         varchar(12)   not null
,col1       varchar(100)      null
,col2       int               null
,col3       varchar(20)       null
,col4       datetime          null
,col5       char(20)          null
,PRIMARY KEY (PK, UpdateDate)
);

insert into dbo.bigtable         values ('20170512', 'ABC', NULL, 6, 'C1', '20161223', 'closed')

insert into dbo.bigtable_archive values ('20170427', 'ABC', NULL, 6, 'C1', '20160820', 'open')
insert into dbo.bigtable_archive values ('20170315', 'ABC', NULL, 5, 'C1', '20160820', 'open')
insert into dbo.bigtable_archive values ('20170212', 'ABC', 'C1', 1, 'C1', '20160820', 'open')
insert into dbo.bigtable_archive values ('20170109', 'ABC', 'C1', 1, 'C1', '20160513', 'open')

insert into dbo.bigtable         values ('20170526', 'XYZ', 'sue', 23, 'C1', '20161223', 're-open')

insert into dbo.bigtable_archive values ('20170401', 'XYZ', 'max', 12, 'C1', '20160825', 'cancel')
insert into dbo.bigtable_archive values ('20170307', 'XYZ', 'bob', 12, 'C1', '20160825', 'cancel')
insert into dbo.bigtable_archive values ('20170223', 'XYZ', 'bob', 12, 'C1', '20160820', 'open')
insert into dbo.bigtable_archive values ('20170214', 'XYZ', 'bob', 12, 'C1', '20160513', 'open')
;

create table #columns
(rid        int           identity(1,1)
,PK         varchar(12)   not null
,UpdateDate datetime      not null
,ColName    varchar(128)  not null
,ColValue   varchar(max)      null
,PRIMARY KEY (rid, PK, UpdateDate, ColName)
);

declare @columns_max varchar(max),
        @columns_raw varchar(max),
        @cmd         varchar(max)

select  @columns_max = stuff((select ',isnull(convert(varchar(max),'+name+'),''NULL'') as '+name
                from    syscolumns
                where   id   = object_id('dbo.bigtable')
                and     name not in ('PK','UpdateDate')
                order by name
                for xml path(''))
            ,1,1,''),
        @columns_raw = stuff((select ','+name
                from    syscolumns
                where   id   = object_id('dbo.bigtable')
                and     name not in ('PK','UpdateDate')
                order by name
                for xml path(''))
            ,1,1,'')

select @cmd = '
insert #columns (PK, UpdateDate, ColName, ColValue)
select PK,UpdateDate,ColName,ColValue
from
(select PK,UpdateDate,'+@columns_max+' from bigtable
 union all
 select PK,UpdateDate,'+@columns_max+' from bigtable_archive
) p
unpivot
  (ColValue for ColName in ('+@columns_raw+')
) as unpvt
order by PK, ColName, UpdateDate'

--select @cmd

execute(@cmd)

--select * from #columns order by rid
;

select  c2.PK, c2.UpDateDate, c2.ColName, c1.ColValue as 'Old Value', c2.ColValue as 'New Value'
from    #columns c1,
        #columns c2
where   c2.rid                       = c1.rid + 1
and     c2.PK                        = c1.PK
and     c2.ColName                   = c1.ColName
and     isnull(c2.ColValue,'xxx')   != isnull(c1.ColValue,'xxx')
order by c1.PK, c1.UpdateDate, c1.ColName
;

View schema
Execution time: 0,09 sec, rows selected: 16, rows affected: 60, absolute service time: 0,25 sec