How to updae table from alv

hi experts.

i have a alv report there is a column updated_by when a record is changed in the report through alv then column updated_by field have to be updated by sy-uname it means the database table has to be updated by sy-uname.

can anybody help me regarding this how to update the column when records are changed with sy-uname if possible with example.

thanks in advance.

regards,

venu.