15. A method comprising: storing, by a processing apparatus comprising one or more computer processors and on a storage apparatus comprising computer memory: a search engine index including searchable content for a plurality of documents, wherein each document is associated with a unique identifier, with a table, and with a join key based upon which the document can be associated with other documents having an identical join key, a join mapping that maps between documents and join keys for a join field, and a bitset index that maps ordinal locations in a join bitset to join keys for a join field; the processing apparatus operating a search engine to execute queries against the search engine index; the processing apparatus receiving a composite join query comprising a specification of a user query, a specification of a root table, a specification of a join table, and a specification of a join field, wherein the specification of the user query comprises one or more Boolean operations applied to one or more unitary queries; for each of the unitary queries, the processing apparatus: executing the unitary query against the search engine index using the search engine, filtering results of the execution of the unitary query for documents contained in at least one of the root table and the join table, and identifying join keys from the join field that correspond to the filtered results by setting bits in a join bitset according to the bitset index; for each of the Boolean operations, the processing apparatus applying the Boolean operation according to the user query to one or more join bitsets, wherein the one or more join bitsets are obtained from executed unitary queries, from other applied Boolean operations or from both, to create a join bitset, until all of the one or more Boolean operations have been applied; the processing apparatus storing the join bitset created from an application of a last one of the one or more Boolean operations; the processing apparatus retrieving a set of documents from the root table; the processing apparatus filtering the set of documents from the root table to obtain a set of documents having join keys that match join keys identified by the stored join bitset; and the processing apparatus providing the filtered set of documents as a result for the composite join query.
15. A method comprising: storing, by a processing apparatus comprising one or more computer processors and on a storage apparatus comprising computer memory: a search engine index including searchable content for a plurality of documents, wherein each document is associated with a unique identifier, with a table, and with a join key based upon which the document can be associated with other documents having an identical join key, a join mapping that maps between documents and join keys for a join field, and a bitset index that maps ordinal locations in a join bitset to join keys for a join field; the processing apparatus operating a search engine to execute queries against the search engine index; the processing apparatus receiving a composite join query comprising a specification of a user query, a specification of a root table, a specification of a join table, and a specification of a join field, wherein the specification of the user query comprises one or more Boolean operations applied to one or more unitary queries; for each of the unitary queries, the processing apparatus: executing the unitary query against the search engine index using the search engine, filtering results of the execution of the unitary query for documents contained in at least one of the root table and the join table, and identifying join keys from the join field that correspond to the filtered results by setting bits in a join bitset according to the bitset index; for each of the Boolean operations, the processing apparatus applying the Boolean operation according to the user query to one or more join bitsets, wherein the one or more join bitsets are obtained from executed unitary queries, from other applied Boolean operations or from both, to create a join bitset, until all of the one or more Boolean operations have been applied; the processing apparatus storing the join bitset created from an application of a last one of the one or more Boolean operations; the processing apparatus retrieving a set of documents from the root table; the processing apparatus filtering the set of documents from the root table to obtain a set of documents having join keys that match join keys identified by the stored join bitset; and the processing apparatus providing the filtered set of documents as a result for the composite join query. 27. The method of claim 15 , wherein the specification of the root table and the specification of the join table are separate from the specification of the user query in the composite join query.