We present an efficient model to retrieve data from a database by implementing plug-and-play queries using the query guards. The model is efficient in the sense that it saves time when writing a query and promotes query portability and reuse. A plug-and-play query is a freestanding query that can couple to any data socket and self determine whether it can be evaluated reliably on the data. We use hierarchies to improve SQL querying in a way that eliminates the need to write a view to construct virtual tables or a set of tables to run a query. The hierarchy is a declarative specification of the desired shape of data rather than a description of how the data is organized. The advantage is that the common use of logical or semantic pointers in the SQL queries is eliminated and a natural way to group data for aggregation is provided. The plug-and-play queries have several advantages, they are portable and can be used to evaluate any data source.