How to use ora_hash on a column of datatype xmltype

Question

I would like to use ORA_HASH on xmltype datatype, and workarounds are straight forward solutions ?

I am using oracle 11g r2 and binary xml as storage option for xmlt

Answer 1

As you already know, ora_hash doesn't accept long or LOB values. You could pass in the first 4k or 32k of the XML content, but if you need to make sure that the entire XML document hasn't changed, that won't be sufficient. And as Ben mentioned, ora_hash has a maximum of 4294967295 buckets, so collisions are rather more likely than with SHA-1 or MD5. As the documentation says, ora_hash 'is useful for operations such as analyzing a subset of data and generating a random sample'.

You can use the dbms_crypto package to hash the whole XMLType value, as a CLOB extracted with the getClobVal function, with a wrapper function to make it simpler to use:

create or replace function my_hash(xml xmltype) return raw is
begin
  return dbms_crypto.hash(src=>xml.getclobval(), typ=>dbms_crypto.hash_sh1);
end;
/

You can then pass in your XMLType, as a value or as a column as part of a select:

select my_hash(xml) from t42;

MY_HASH(XML)                                 
---------------------------------------------
494C4E7688963BCF312B709B33CD1B5CCA7C0289