update T1 set C1="xx" where C2 in (1, 2, 3, 4, 5);
update T2 set C3="yy", C4="zz" where C2 in (1, 2, 3, 4, 5);
....

DECLARE TYPE some_var (1,2,3,4,5);
BEGIN
update T2 set C3="yy", C4="zz" where C2 in (some_var);
END;

CREATE OR REPLACE FUNCTION Split
(
   PC$Chaine IN VARCHAR2,         -- input string
   PN$Pos IN PLS_INTEGER,         -- token number
   PC$Sep IN VARCHAR2 DEFAULT ',' -- separator character
)
RETURN VARCHAR2
IS
  LC$Chaine VARCHAR2(32767) := PC$Sep || PC$Chaine ;
  LI$I      PLS_INTEGER ;
  LI$I2     PLS_INTEGER ;
BEGIN
  LI$I := INSTR( LC$Chaine, PC$Sep, 1, PN$Pos ) ;
  IF LI$I > 0 THEN
    LI$I2 := INSTR( LC$Chaine, PC$Sep, 1, PN$Pos + 1) ;
    IF LI$I2 = 0 THEN LI$I2 := LENGTH( LC$Chaine ) + 1 ; END IF ;
    RETURN( SUBSTR( LC$Chaine, LI$I+1, LI$I2 - LI$I-1 ) ) ;
  ELSE
    RETURN NULL ;
  END IF ;
END;


CREATE OR REPLACE FUNCTION Dynamic_In ( PC$list IN VARCHAR2 )
RETURN sys.dbms_debug_vc2coll
IS
  ttab sys.dbms_debug_vc2coll := sys.dbms_debug_vc2coll() ;
  LC$Token  VARCHAR2(100) ;
  i         PLS_INTEGER := 1 ;
BEGIN
  -- Populate the collection --
  LOOP
    LC$Token := Split( PC$List, i , ',') ;
    EXIT WHEN LC$Token IS NULL ;
    ttab.extend ;
    ttab(ttab.COUNT) := LC$Token ;
    i := i + 1 ;
  END LOOP ;
  RETURN ttab ;
END ;

BEGIN
DECLARE LC$List  Varchar2(100) := '1, 2, 3';
    update T set C1='xx' where C2 in (SELECT * FROM TABLE( CAST ( Dynamic_In(LC$List) AS sys.dbms_debug_vc2coll ) )  );

END;