postgres function is not executing properly

Question

Here I have used like this but not working please provide me the solution

  IF  'select topic1 from tblscmipklimipcmapprovalio2269 t except select miptopic1 from tblmiptopic1master tm'    THEN
      BEGIN
          topic := topic1;
              execute 'insert into tblmiptopic1master (miptopic1 , createdby , createdon , updatedby , updatedon , active) values 
  (topic,22,'',55,'',1)';
          
      END;
  ```

Answer 1

insert into tblmiptopic1master
  (miptopic1, createdby, createdon, updatedby, updatedon, active)       
select topic1, 22, '', 55, '', 1
from tblscmipklimipcmapprovalio2269 t
where not exists ( 
   select * from tblmiptopic1master nx
   where nx.miptopic1 = t.topic1
   );     

Answer 2

If you want the topic to be unique, then you should let the database control the data integrity:

alter table tblmiptopic1master add constraint unq_tblmiptopic1master_miptopic1
    unique (miptopic1);

Then you would phrase the insert as:

insert into tblmiptopic1master (miptopic1, createdby, createdon, updatedby, updatedon, active)       
    select topic1, 22, '', 55, '', 1
    from tblscmipklimipcmapprovalio2269 t
    on conflict (miptopic1) do nothing;