Merge Statement Example in Orcale

merge [ hints ] into table-name-1 | view-name-1 [ alias-1 ]
using table-name-2 | view-name-2 | subquery [ alias-2 ]
on ( condition )
[ merge-update-clause ] [ merge-insert-clause ] [ error-logging-clause ];
 

 create table table_dest (
  id number primary key,
  txt varchar2(20)
);

insert into table_dest values (1,'one');
insert into table_dest values (3,'three');
insert into table_dest values (5,'five');

commit;

create table table_source (
  id number primary key,
  txt varchar2(20)
);

insert into table_source values (2,'TWO');
insert into table_source values (3,'THREE');

commit;

merge into
  table_dest d
using
  table_source s
on
  (s.id = d.id)
when matched then update set d.txt = s.txt
when not matched then insert (id, txt) values (s.id, s.txt);

select * from table_dest;

  ID TXT
---------- --------------------
  1 one
  3 THREE
  5 five
  2 TWO

 It is not possible to update a field in the destination table that is used to merge with the source table.

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