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Comparison for Sorting

Above assumes that we have a function to compare tuples.

Needs to understand ordering on different data types.

E.g. a function tupCompare(r1,r2,f) (cf. C's strcmp)

  • takes two tuples r1, r2 and a field name f
  • returns negative value if r1.f < r2.f
  • returns positive value if r1.f > r2.f
  • returns zero value if r1.f == r2.f
Can work on multiple attributes (sort on first, then second if equal, ...) 

-- example multi-attribute sort
select * from Students
order by age desc, year_enrolled