Oracle PL/SQL/PL SQL/Constant Number

Change constant number

 
SQL>
SQL> -- change constant number
SQL>
SQL>  declare
  2      myconstant constant number := 50;
  3    begin
  4      myconstant := 51;
  5    end;
  6    /
    myconstant := 51;
    *
ERROR at line 4:
ORA-06550: line 4, column 5:
PLS-00363: expression "MYCONSTANT" cannot be used as an assignment target
ORA-06550: line 4, column 5:
PL/SQL: Statement ignored

SQL>

Declare initialized constant number

 
SQL>
SQL>
SQL>
SQL> -- declare initialized constant number
SQL>
SQL>   declare
  2      l_number_constant  constant number := 50;
  3    begin
  4      null;
  5      dbms_output.put_line(l_number_constant);
  6    end;
  7    /
50
PL/SQL procedure successfully completed.
SQL>
SQL>

declare number constant uninitialized

  
SQL>
SQL>  declare
  2      myNumber_constant constant number;
  3    begin
  4      null;
  5    end;
  6    /
    myNumber_constant constant number;
    *
ERROR at line 2:
ORA-06550: line 2, column 5:
PLS-00322: declaration of a constant "MYNUMBER_CONSTANT" must contain an initialization assignment
ORA-06550: line 2, column 23:
PL/SQL: Item ignored

SQL>

This script demonstrates constants

   
SQL>
SQL>
SQL> SET SERVEROUTPUT ON
SQL>
SQL>
SQL> DECLARE
  2      fnameValue CONSTANT VARCHAR2(50) := "Ron";
  3   BEGIN
  4      fnameValue := "AAA";
  5   EXCEPTION
  6      WHEN OTHERS
  7      THEN
  8         DBMS_OUTPUT.PUT_LINE(SQLERRM);
  9   END;
 10   /
    fnameValue := "AAA";
    *
ERROR at line 4:
ORA-06550: line 4, column 5:
PLS-00363: expression "FNAMEVALUE" cannot be used as an assignment target
ORA-06550: line 4, column 5:
PL/SQL: Statement ignored

SQL>

you must initialize the constant at the time of declaration

  
SQL>
SQL>
SQL> declare
  2    myNumber_constant constant number := 50;
  3  begin
  4    null;
  5  end;
  6  /
PL/SQL procedure successfully completed.
SQL>
SQL>