16. The system of claim 13 , wherein the query optimizer is to request a query policy without having to issue pre-queries such that analytical determinations are made and then stored and specified for one or more locations of data via a customer schema.
13. A system comprising: a processor and a memory; a communications interface to a database system having a relational data store and a non-relational data store implemented therein; a request processor to receive a request at the host system for a database system, the request specifying data for retrieval from the database system; a customer schema processor to retrieve, based on the request, one or more locations of the data for retrieval; a query layer agent to generate a database query based on the request, wherein the database query specifies a plurality of data elements for retrieval, the plurality of data elements including one or more data elements residing within a non-relational data store and one or more other data elements residing within a relational data store; a query optimizer to optimize the database query to include at least a sub-query or a pre-query; wherein the query layer agent to execute the optimized database query against the database system to retrieve the data; wherein the query optimizer to further: (i) identify via a first sub-query to a table within relational data store, the first portion of the data for retrieval, (ii) identify via a second sub-query to the non-relational data store, the second portion of the data for retrieval, (iii) identify a data delta between the first sub-query that identifies the first portion of the data retrieved within the relational data store and the second sub-query that identifies the second portion of the data retrieved within the non-relational data store, and (iv) execute a third sub-query to replicate missing data from the relational data store to the non-relational data store according to the data delta; wherein the database query comprises a join operation performed by initiating non-relational database queries on the non-relational data store where one or more foreign key parents are stored in the relational data store; and wherein the join operation comprises a plurality of sub-queries which are generated based on query optimizations available via an optimizer agent of the host organization, the query optimizations selected from the group comprising: a specified ordering for the plurality of sub-queries; a target data store for execution of a corresponding sub-query; one or more pre-query assessments based on the data for retrieval; a replication order from the relational data store to the non-relational data store; and an in-memory join operation specifying at least one or more of the plurality of data elements for retrieval from each of the relational data store and the non-relational data store and placed into memory accessible to the optimizer agent and a corresponding sub-query to retrieve the at least one or more of the plurality of data elements from the memory accessible to the optimizer agent in fulfillment of the request.