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Joins

Nested Loops Join

Simple improvement:

It is easy to reduce the number of scans of S (inner loop).

Original algorithm


for each row r in R:
    for each row s in S:
        if match(r, s):
            output join(r, s)

Equivalent algorithm


for each page p in R:
    for each row r in p:
        for each row s in S:
            if match(r, s):
                output join(r, s)

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