The following anonymous PL/SQL block copies a 
LONG column from table LONGTABLE into a VARCHAR2 column from table VARCHARTABLE, with the assumption 
that LONGTABLE.LONGCOLUMN does not exceed 4000 bytes
in length: 

declare 
string varchar2(4000); 
character char(1); 
begin 
select longcolumn, pk into string, character from longtable; 
insert into varchartable values (string, character); 
end; 

Notice that, even though a varchar2 
datatype declaration in PL/SQL can take a 
maximum length value of up to 32767, the actual VARCHAR2 datatype in the database can only 
accomodate up to 4000 bytes(in 8). 

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