SQL
Anomalies and Denormalisation
The three anomalies normalisation prevents, and the disciplined way to reintroduce redundancy when reads genuinely demand it.
#Normalisation
Normal forms and functional dependencies.
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SQL
BCNF and Functional Dependencies
The formal notation behind normalisation, and the stricter normal form that catches what 3NF allows through when candidate keys overlap.
SQL
First, Second and Third Normal Form
Normalisation worked through on one table: remove repeating groups, then partial dependencies, then transitive ones - with the SQL at each step.
SQL
Data Integrity, Redundancy and Consistency
The three kinds of integrity a relational database enforces, why redundancy causes anomalies, and where a derived value is worth its maintenance cost.