1. A method for processing database queries, comprising: encrypting a database in a database system using two or more encryption schemes, with each data item in the database encrypted using at least one of the two or more encryption schemes; selecting for each data item specified in an input query from an application, one of the encryption schemes; transforming the input query to an encrypted query using the selected encryption scheme for each data item specified in the query; executing the encrypted query at the database system, without decrypting any of the encrypted data items to plaintext at the database system, to produce one or more encrypted results; decrypting the encrypted results using the selected decryption scheme for each data item in the encrypted results to generate decrypted results; and returning the decrypted results to the application.