01
The Relational Model
The rationale for the move from a file to a database, the relation–row–column–domain concepts, key types, integrity constraints, the three-valued logic of null values, and data type selection.
- 01 What Is a Database The search, concurrency, and integrity problems created by keeping data in a file, and which of these a database management system solves and with what guarantees.
- 02 The Relational Model The definition of relation, row, column, and domain; where row order and row repetition stand in the model, and where a SQL table departs from a relation.
- 03 Keys Definitions of superkey, candidate key, primary key, alternate key, and foreign key; the choice between a natural and a surrogate key, and the criteria for choosing a key.
- 04 Integrity Constraints The definitions of domain, entity, and referential integrity; a foreign key's delete and update actions; the timing of constraint checking and the case for writing a constraint into the schema.
- 05 Null Values Why null is not a value, the truth table of three-valued logic, how filters and NOT IN behave with nulls, how a uniqueness constraint treats a null, and ways to avoid null values.
- 06 Data Types The choice among integer, decimal, and floating-point numbers; text length and collation; storing dates alongside a time zone; binary data, truth values, and enumeration patterns.