17.5. JOINs by Function Calls
JOINs can also be done inside functions that relate columns from one or more tables in their parameters. This is easier to explain with an actual example, from John Botibol of Deverill plc in Dorset, U.K. His problem was how to “flatten” legacy data stored in a flat file database into a relational format for a data warehouse. The data included a vast amount of demographic information on people, related to their subjects of interest. The subjects of interest were selected from a list; some subjects required just one answer, and others allowed multiple selections.
The problem was that the data for multiple selections was stored as a string with a one or a zero in positional places to indicate “interested” or “not ...
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