how to make selecting random rows in oracle faster with table with millions of rows

Question

Is there a way to make selecting random rows faster in oracle with a table that has million of rows. I tried to use sample(x) and dbms_random.value and its taking a long time to

Answer 1

Here's the same question on AskTom:

http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:6075151195522

If you know how big your table is, use sample block as described above. If you don't, you can modify the routine below to get however many rows you want.

Copied from: http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:6075151195522#56174726207861

create or replace function get_random_rowid
( table_name varchar2
) return urowid
as
sql_v varchar2(100);
urowid_t dbms_sql.urowid_table;
cursor_v integer;
status_v integer;
rows_v integer;
begin
  for exp_v in -6..2 loop
    exit when (urowid_t.count > 0);
    if (exp_v < 2) then
      sql_v := 'select rowid from ' || table_name
      || ' sample block (' || power(10, exp_v) || ')';
    else
      sql_v := 'select rowid from ' || table_name;
    end if;
    cursor_v := dbms_sql.open_cursor;
    dbms_sql.parse(cursor_v, sql_v, dbms_sql.native);
    dbms_sql.define_array(cursor_v, 1, urowid_t, 100, 0);
    status_v := dbms_sql.execute(cursor_v);
    loop
      rows_v := dbms_sql.fetch_rows(cursor_v);
      dbms_sql.column_value(cursor_v, 1, urowid_t);
      exit when rows_v != 100;
    end loop;
    dbms_sql.close_cursor(cursor_v);
  end loop;
  if (urowid_t.count > 0) then
    return urowid_t(trunc(dbms_random.value(0, urowid_t.count)));
  end if;
  return null;
exception when others then
  if (dbms_sql.is_open(cursor_v)) then
    dbms_sql.close_cursor(cursor_v);
  end if;
  raise;
end;
/
show errors