Varieties of Selection (cont)
One-dimensional selection queries = condition on single attribute.
- one:
select * from R where k = val
where k is a unique attribute and val is a constant
- pmr:
select * from R where k = val
where k is non-unique and val is a constant
- range:
select * from R where k ≥ lo and k ≤ hi
where k is any attribute and lo and hi are constants
either lo or hi may be omitted for open-ended range
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