SQL：通过联接将数据从一列复制到同一表中的另一列，然后删除

Question

I 'm getting errors when I try to copy data from 1 column to another, since there are 2 rows with almost same data but diff unique IDs. I used the select statement which works fine to select the specific dates to be copied to the del_date column from train_date but the condition in where statement. How can I copy the data to the del date and then delete the train_date rows. Thanks

update dbo.Comp d
  set d.del_date =  t.train_date 
  (
   SELECT d.unique_id as delUnique
      ,t.unique_id  as TraUnique
      ,d.del_date as delDelDate
      ,t.del_date as traDelDate
      ,d.train_date as delTrainDt
      ,t.train_date as traTrainDt

  FROM dbo.Comp d 
  inner join dbo.Comp t on d.g_id = t.g_id 
  where t.del_date = d.train_date
  and t.unique_id <> d.unique_id
  order by d.og_id, d.g_id

Answer 1

Try this,

update d
set d.del_date =  t.train_date 
FROM dbo.Comp d 
inner join dbo.Comp t on d.g_id = t.g_id 
where t.del_date = d.train_date
and t.unique_id <> d.unique_id