ORA_HASH函数使用的算法是什么?

it can be successfully executed from Oracle. But, as you see, signature a bit differs from ora_hash in Oracle. This function accepts value, its length and initval (may be seed) while signature in Oracle is ora_hash(expr, max_bucket, seed_value).

让我们尝试测试甲骨文

SQL> select ora_hash(utl_raw.cast_to_raw('0'), power(2, 32) - 1, 0) oh1,
  2         ora_hash('0', power(2, 32) - 1, 0) oh2,
  3         ora_hash(0, power(2, 32) - 1, 0) oh3,
  4         ora_hash(chr(0), power(2, 32) - 1, 0) oh4
  5    from dual;

       OH1        OH2        OH3        OH4
---------- ---------- ---------- ----------
3517341953 3517341953 1475158189 4056412421

C

int main()
{
    ub1 ta[] = {0};
    ub1* t = ta;
    cout << hash(t, 1, 0) << endl;
    ub1 ta0[] = {'0'};
    ub1* t0 = ta0;
    cout << hash(t0, 1, 0) << endl;
    return 0;
}

1843378377
4052366646

没有一个数字匹配.那么问题出在哪里呢?ora_hash 接受几乎任何类型的参数(例如 select ora_hash(sys.odcinumberlist(1,2,3)) from dual)，而 C 函数接受作为字节数组的值.这意味着在函数调用之前会发生一些转换.因此，在使用提到的 C 哈希函数之前，您必须弄清楚实际值在传递给它之前是如何转换的.

SQL> select dbms_utility.get_hash_value('0', 0 + 1, 1e6 + 1) ha1,
  2         ora_hash('0', 1e6, 0) + 1 ha2
  3    from dual;

       HA1        HA2
---------- ----------
    338437     338437

  function get_hash_value(name varchar2, base number, hash_size number)
    return number is
  begin
    return(icd_hash(name, base, hash_size));
  end;

  function icd_hash(name      varchar2,
                    base      binary_integer,
                    hash_size binary_integer) return binary_integer;
  pragma interface(c, icd_hash);