Extract of LONG

Question

Hello everybody,
I am a problem, with the Oracle's Function.
I create a table A : CREATE TABLE A (id NUMBER, name LONG);
I want extract from the characters of 'name'. I use the function SUBSTR : SELECT SUBSTR(name,1,2) FROM A;
However, Oracle produce a error : ORA-00932: types de données incohérents ; attendu : NUMBER ; obtenu : LONG.
How that this fact that I cannot have a result? However, LENGTH is character strings.

Answer 1

maybe this example might be of some help.
CREATE OR REPLACE Function convert_long_to_char( pTableName in varchar2,
                                                 pColumnName in varchar2,
                                                 pRowId in rowid ) return varchar2 As
  vCursor    integer default dbms_sql.open_cursor;
  vN         number;
  vLongVal  varchar2(4000);
  vLongLen  number;
  vBuflen    number := 4000;
  vCurPos    number := 0;
begin
  dbms_sql.parse( vCursor,'select ' || pColumnName || ' from ' || pTableName ||
                                                          ' where rowid = :x',
                  dbms_sql.native );
  dbms_sql.bind_variable( vCursor, ':x', pRowId );
  dbms_sql.define_column_long(vCursor, 1);
  vN := dbms_sql.execute(vCursor);
  if (dbms_sql.fetch_rows(vCursor)>0) then
    dbms_sql.column_value_long(vCursor, 1, vBuflen, vCurpos ,
                               vLongVal, vLongLen );
  end if;
  dbms_sql.close_cursor(vCursor);
  return vLongVal;
end convert_long_to_char;
SQL> describe long_tab;
Name                                      Null?    Type
PCOL                                               LONG
SQL> select * from long_tab;
no rows selected
SQL> insert into long_tab
  2  values
  3  ('1234567890 ABCDEFGHIJLKMNOPQRSTUVWXYZ '||
  4   '0987654321 POIUYTREWQASDFGHJKLMNBVCXZ '||
  5   '1029384756 QWERTYUIOPASDFGHJKLZXCVBNM '||
  6   '1357924680 QAZWSXEDCRFVTGBYHNUJMIKOLP '||
  7   '2468013579 MNBVCXZLKJHGFDSAPOIUYTREWQ '||
  8   '2143658709 ZXCVBNMLKJHGFDSAQWERTYUIOP '||
  9   '5647382910 QAWSEDRFTGYHUJIKOLPMNBVCXZ '||
10   '1029384765 ZXASQWERDFCVBNGHTYUIJKMLOP '||
11   '3142758609 IKLOPMJUYHNBGTRFVCDEWSXZAQ '||
12   '6789054321 TGBVFREDCXSWQAZYHNMJUIKLOP');
1 row created.
SQL> commit;
Commit complete.
SQL> select * from long_tab;
PCOL
1234567890 ABCDEFGHIJLKMNOPQRSTUVWXYZ 0987654321 POIUYTREWQASDFGHJKLMNBVCXZ 1029
SQL> select convert_long_to_char('long_tab','pcol',rowid) pcol
  2    from long_tab;
PCOL
1234567890 ABCDEFGHIJLKMNOPQRSTUVWXYZ 0987654321 POIUYTREWQASDFGHJKLMNBVCXZ 1029
384756 QWERTYUIOPASDFGHJKLZXCVBNM 1357924680 QAZWSXEDCRFVTGBYHNUJMIKOLP 24680135
79 MNBVCXZLKJHGFDSAPOIUYTREWQ 2143658709 ZXCVBNMLKJHGFDSAQWERTYUIOP 5647382910 Q
AWSEDRFTGYHUJIKOLPMNBVCXZ 1029384765 ZXASQWERDFCVBNGHTYUIJKMLOP 3142758609 IKLOP
MJUYHNBGTRFVCDEWSXZAQ 6789054321 TGBVFREDCXSWQAZYHNMJUIKLOP
SQL>