Fig. 18.6 shows some sample data for Student and Option tables that record which
modules each student is studying at a college. Suppose there are 500 rows in Student
and 4000 rows in Option.
The optimiser accepts a query language command (typically an SQL command, see
Chapter 19) and breaks it down into an equivalent set of relational algebra operations.
It needs to find an efficient sequence of operations, taking advantage of its knowledge
of the database storage structures and other properties of the data.
Query optimisation is a specialist subject. We will look at only a few of the options
available. In order to compare different query ...
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