表内复制列

declare @tableA as table(
    item_name varchar(50),
    item_cname nvarchar(50)
)

insert @tableA (item_name, item_cname)
select  b.item_name, a.item_cname
 from [Tg_ExcelImport] a, Tg_ExcelImport b 
 where a.table_name = 'tg_staffinfo' and  b.table_name = 'tg_staffinfo_temp' and a.item_name = b.item_name
 
 update [Tg_ExcelImport] set item_cname =  (select item_cname from @tableA a
  where a.item_name = Tg_ExcelImport.item_name and Tg_ExcelImport.table_name = 'tg_staffinfo_temp')