Suppose that a relation factory contains 800 tuples and Each tuple is comprised of a header: Database Systems Coursework, UOS, UK

University University Of Salford (UOS)
Subject Database Systems

Assessment set by Dr. Bryant

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Questions

1) (a) Suppose that a relation factory contains 800 tuples. Each tuple is comprised of a header (24 bytes) and four attributes: ID (5 bytes), name (10 bytes), street (20 bytes), and postcode (6 bytes). The size of each disc block is 1024 bytes and the size of the header of each disc block size 24 bytes.

(i) How many blocks would be required to store the whole of this relation?

(ii) How many blocks would be required to store a projection that does not include the attribute street?

(iii) Explain why such a projection could be used to optimize a query whose
results do not include data for the attribute street.

(b) Consider the SQL query shown in Table 1.
(i) Draw a near-optimal query tree for the SQL query.

(ii) Identify the root and leaf nodes in the tree that you drew for part (i).

(iii) Write down a justification for the position of the root node and each of the internal nodes in the tree that you drew for part (i) in terms of the heuristic steps that optimizers apply to reduce the cost of optimization. Explain why the position of the nodes should make the query efficient.

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