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Query Evaluation in CoDbs

Projection is easy if one slice contains all required attributes.

If not ...

  • sequential scan of relevant slices in parallel
  • combine values at each iteration to form a tuple
Example: select a,b,c from R(a,b,c,d,e) 

Assume: each column contains N values
for i in 0 .. N-1 {
   x = a[i]   // i'th value in slice containing a
   y = b[i]   // i'th value in slice containing b
   z = c[i]   // i'th value in slice containing c
   add (x,y,z) to Results
}