问题
Is there any method in SQL (Oracle) using which I can get something like:
select checksum(select * from table) from table;
回答1:
You can use DBMS_SQLHASH.GETHASH for this. The query results must be ordered and must not contain any LOBs, or the results won't be deterministic.
select dbms_sqlhash.gethash(q'[select * from some_table order by 1,2]', digest_type => 1)
from dual;
Where digest_type 1 = HASH_MD4, 2 = HASH_MD5, 3 = HASH_SH1.
That package is not granted to anyone by default. To use it, you'll need someone to logon as SYS and run this:
SQL> grant execute on dbms_sqlhash to <your_user>;
The query results must be ordered, as described in "Bug 17082212 : DBMS_SQLHASH DIFFERENT RESULTS FROM DIFFERENT ACCESS PATH".
I'm not sure why LOBs don't work, but it might be related to the way the function ORA_HASH does not work well with LOBs. This Jonathan Lewis article includes some examples of ORA_HASH returning different results for the same LOB data. And recent versions of the SQL Language Reference warn that ORA_HASH does not support LOBs.
来源：https://stackoverflow.com/questions/40699076/oracle-get-checksum-value-for-a-data-chunk-defined-by-a-select-clause