For Oracle TDE, there is both the option to add salt to plaintext (by default) or to ignore salt (using the NO SALT) parameter.
- I wanted to know if salt is unique per row/record in a table or common across all rows in a single table.
- Is there any way to see the encrypted value as the result of a query ? (Opening the wallet gives you the actual de-encrypted value, and I'm getting an error trying to query without opening the wallet and setting the master key).
Regarding your questions:
If you want to have the option to query the data at will, with or without encryption and without depending of a wallet, you can use DBMS_CRYPTO in a package to store the data using function to encrypt or decrypt at will. You have a good example of this last point here
https://oracle-base.com/articles/10g/database-security-enhancements-10g#dbms_crypto