Question

Suppose I have an oracle table with two columns: type varchar2 and data varchar2. I want to know if there is a somewhat efficient way in plsql or straight oracle sql to compute a hash over all the data column (ideally sha1, but md5 or custom oracle hash functions are acceptable). For example, a mysql implementation of the solution might look like:

mysql dialect query:
select type, sha1(group_concat(data order by data separator '')) data_hash from my_table group by type

example output:    
+------+------------------------------------------+
| type | data_hash                                |
+------+------------------------------------------+
| a    | dbe343bfc23545c72f11fc7d2433df3263a71d0d |
| b    | b2baee034a7ed3aa1fa1bd441e141909f1b2f57c |
+------+------------------------------------------+

I’d prefer a straight query over a cursor iteration, and sha1 over other hashes.

Answer 1

You could try

SELECT type, SUM(ORA_HASH(data)) FROM my_table GROUP BY type

Oracle does have a COLLECT but that doesn’t work with ORA_HASH. In 11g you can do

select deptno, ora_hash(listagg(ename) within group (order by ename))
from emp
group by deptno