July 2010
Intermediate to advanced
840 pages
16h 33m
English
Content preview from Joe Celko's SQL for Smarties, 3rd Edition
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2.6. Boyce-Codd Normal Form (BCNF)
A table is in BCNF when for all nontrivial FDs (X → A), X is a superkey for the whole schema. A superkey is a unique set of columns that identify each row in a table, but you can remove some columns from it and it will still be a key. Informally, a superkey is carrying extra weight.
BCNF is the normal form that actually removes all transitive dependencies. A table is in BCNF if for all (X → Y), X is a key—period. We can go to this normal form just by adding another key with UNIQUE (room, time_period) constraint clause to the table Classes.
There are some other interesting and useful “higher” normal forms, but they are outside of the scope of this discussion. In our example, we have removed all of the important ...
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