貌似to_clob也不行，看看tom这个

You Asked

Can you perform string functions on the datatype LONG?

and we said...

In PLSQL yes -- in SQL no.

If the long is 32k or less, you can do some interesting things in PLSQL.  Lets say you

have a table T with a long column like this:

ops$tkyte@8i> create table t ( x int, y long );

Table created.

ops$tkyte@8i> insert into t values ( 1, 'how now brown cow' );

1 row created.

ops$tkyte@8i> select substr( y, 1, 5 ) from t;

select substr( y, 1, 5 ) from t

*

ERROR at line 1:

ORA-00932: inconsistent datatypes

ops$tkyte@8i> create or replace function t_substr

( p_rowid in rowid,

p_from in number,

p_for in number ) return varchar2

2  as

3          l_str   long;

4  begin

5          select y into l_str from t where rowid = p_rowid;

6

7          return substr( l_str, p_from, p_for );

8  end;

9  /

Function created.

ops$tkyte@8i> select t_substr( rowid, 1, 5 ) from t;

T_SUBSTR(ROWID,1,5)

------------------------------

how n

So, for longs that are 32k or less, we can write functions that are callable in SQL to

allow us to do some operations on these long columns.

Additionally -- we can use dbms_sql to READ longs (but not write) them that are of any

size.  We would piecewise read them.  You cannot call a function that uses dbms_sql from

SQL as  did above but you can use it in any other procedure/function you write.  Here is

an example of a piecewise read of a long in plsql:

create or replace procedure showlong( p_query in varchar2 )

as

l_cursor    integer default dbms_sql.open_cursor;

l_n         number;

l_long_val  varchar2(250);

l_long_len  number;

l_buflen    number := 250;

l_curpos    number := 0;

begin

dbms_sql.parse( l_cursor, p_query, dbms_sql.native );

dbms_sql.define_column_long(l_cursor, 1);

l_n := dbms_sql.execute(l_cursor);

if (dbms_sql.fetch_rows(l_cursor)>0)

then

loop

dbms_sql.column_value_long(l_cursor, 1, l_buflen, l_curpos ,

l_long_val, l_long_len );

l_curpos := l_curpos + l_long_len;

dbms_output.put_line( l_long_val );

exit when l_long_len = 0;

end loop;

end if;

dbms_output.put_line( '====================' );

dbms_output.put_line( 'Long was ' || l_curpos || ' bytes in length' );

dbms_sql.close_cursor(l_cursor);

exception

when others then

if dbms_sql.is_open(l_cursor) then

dbms_sql.close_cursor(l_cursor);

end if;

htp.preClose;

raise;

end showlong;

/

set echo on

begin

showlong( 'select text from all_views where rownum = 1' );

end;

/