SQL> desc TABLE_STEP_INST234
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 NUM_PENDING_PREREQS                       NOT NULL NUMBER(10)
 OBJID                                     NOT NULL VARCHAR2(31)
 OUTFLOW_BITS                                       NUMBER(19)
 PARAMS                                             CLOB
 PARENT2PROC_INST                          NOT NULL VARCHAR2(31)
 ROOT2PROC_INST                            NOT NULL VARCHAR2(31)
 START_TIME                                         DATE
 STATUS                                    NOT NULL NUMBER(2)
 

SQL>
SQL> select sum(dbms_lob.getlength (PARAMS)) from TABLE_STEP_INST234;

SUM(DBMS_LOB.GETLENGTH(PARAMS))
-------------------------------


SQL>

08:20:22 SQL> DESC DBADMIN.CLOB_TEST
 Name					   Null?    Type
 ----------------------------------------- -------- ----------------------------
 NO						    NUMBER
 NAME						    CLOB

08:21:46 SQL> select COUNT(*) from DBADMIN.CLOB_TEST WHERE NAME IS NOT NULL;

  COUNT(*)
----------
      1000

08:22:02 SQL> select sum(dbms_lob.getlength (NAME)) from DBADMIN.CLOB_TEST;

SUM(DBMS_LOB.GETLENGTH(NAME))
-----------------------------
			28000

08:22:13 SQL>