SQLite Export Import
An exporter is being developed in trunk/src/plugins/export/ExportSql.py You can export most of GRAMPS through an SQL Export using the Export Assistant. (Currently, the selection options are ignored, and it will output everything).
SQL stands for "Structured Query Language" and is pronounced "sequel" (it is a joke: as it came after QUEL, it is its sequel). After you export your GRAMPS data into a file such as Untitled_1.sql using the above Exporter, then you can use SQL queries like:
$ sqlite3 Untitled_1.sql SQLite version 3.5.9 Enter ".help" for instructions sqlite> .tables dates family names people repository events media notes places sources sqlite> .headers on .headers on sqlite> select * from people; handle|gramps_id|gender|death_ref_index|birth_ref_index|change|marker0|marker1|private b247d7186567ff472ef|I0000|1|-1|-1|1225135132|-1||0 sqlite> select * from names where surname like "%Smith%"; private|first_name|surname|suffix|title|name_type0|name_type1|prefix|patronymic|group_as|sort_as|display_as|call 0|Test|Smith|||2|||||0|0| sqlite> .exit $
The current database in GRAMPS would require that you write some code to do this, and you'd need to know some details about the data.