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N-d Queries and Indexes

Generalised view of pmr and space queries: 

select * from R
where  a1 op1 C1 and ... and an opn Cn

pmr : all opi are equality tests.     space : some opi are range tests.

Possible approaches to handling such queries ...

  1. use index on one ai to reduce tuple tests
  2. use indexes on all ai, and intersect answer sets