Error in cast a variable

Question

these are few lines from my long STORED PROCEDURE actually i am new to oracle 11g please
declare
v_s nvarchar2(10);
p_RN nvarchar2(10);
begin
v_s := v_s || cast(p_RN as nvarchar2(10)); - ERROR IS COMING IN THIS LINE
end;
error
ORA-06550: line 5, column 39:
PLS-00103: Encountered the symbol "(" when expecting one of the following:
06550. 00000 - "line %s, column %s:\n%s"
*Cause:    Usually a PL/SQL compilation error.
*Action:
please somebody help me

Answer 1

Just a little explanation about the error message.
ORA-06550: line 5, column 39:
PLS-00103: Encountered the symbol "(" when expecting one of the following:
Line 5 column 39 is the starting parenthesis of the "(10)". For using cast you can't add a lenght to the datatype.
If you change that, then you get a different error message:
declare
v_s nvarchar2(10);
p_RN varchar2(10);
begin
  v_s := v_s || cast(p_RN as nvarchar2); -- ERROR IS COMING IN THIS LINE
end;
Fehler beim Start in Zeile 13 in Befehl:
declare
v_s nvarchar2(10);
p_RN varchar2(10);
begin
  v_s := v_s || cast(p_RN as nvarchar2); -- ERROR IS COMING IN THIS LINE
end;
Fehlerbericht:
ORA-06550: line 5, column 22:
PLS-00382: expression is of wrong type
ORA-06550: line 5, column 3:
PL/SQL: Statement ignored
06550. 00000 -  "line %s, column %s:\n%s"
*Cause:    Usually a PL/SQL compilation error.
*Action:ORA-06550: line 5, column 22:
PLS-00382: expression is of wrong type
This shows that you can't convert/cast a nvarchzar type into another nvarchar type.
It would work if you cast a number into a varchar2 type for example
declare
v_s nvarchar2(10);
p_RN number(10);
begin
  v_s := v_s || cast(p_RN as nvarchar2); -- ERROR IS COMING IN THIS LINE
end;
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