oracle long 转换 varchar类型

create or replace function getlong( p_tname in varchar2,p_cname in varchar2,p_con in varchar2, p_value in varchar2 ) 
  return varchar2
as
  l_cursor integer default dbms_sql.open_cursor;
  l_n number;
  l_long_val varchar2(4000);
  l_long_len number;
  l_buflen number := 4000;
  l_curpos number := 0;
begin
 dbms_sql.parse( l_cursor, 'select ' || p_cname || ' from ' || p_tname ||' where '||p_con||' = :x', dbms_sql.native );
 dbms_sql.bind_variable( l_cursor, ':x', p_value );

 dbms_sql.define_column_long(l_cursor, 1);
 l_n := dbms_sql.execute(l_cursor);

 if (dbms_sql.fetch_rows(l_cursor)>0) then
  dbms_sql.column_value_long(l_cursor, 1, l_buflen, l_curpos , l_long_val, l_long_len );
 end if;
 
 dbms_sql.close_cursor(l_cursor);
 return l_long_val;
end getlong;
/ 

--支持view 
SELECT getlong('USER_CONSTRAINTS','SEARCH_CONDITION','CONSTRAINT_NAME',CONSTRAINT_NAME) , tt1.* FROM user_constraints tt1 WHERE tt1.table_name IN ('STOGLD')  ;

--支持table 
create table t ( x long );

declare
data long default rpad( '*', 32000, '*' );
begin
insert into t values ( data );
end;
/


--查询语句

select getlong('test', 'zd','rowid', rowid) from test;--test(表名)，zd(long字段)