Systems Analysis and Synthesis

C.6. Chapter 6

1. On page 192 we discussed a query that could produce a list of timetable clashes . It was suggested that only a very clever optimiser would spot that a cross join was being made between two identical sets of data.

    Suppose that the DBMS’s query optimiser proves inadequate and the resulting query takes too long. It is decided to write an embedded SQL procedure to create the cross join from a single instance of the data. This would involve fetching a list of enrolments for one candidate at a time, storing them in an array — ten locations would be more than enough — and inserting all the required pairs into a new table. Write a query that will produce the required lists of enrolments.

or

2. Candidate C is enrolling in subjects ...