Database basics

Structured collections#

A database stores organized data so applications can retrieve and update it consistently. In a relational database, a table represents a type of thing, a row represents one record, and a column represents one defined attribute.

For a lesson catalog, one row might represent a lesson, while columns store its title, subject, and publication status.

Keys and relationships#

A primary key uniquely identifies a record. A foreign key can refer to a record in another table, allowing relationships without repeatedly copying all details.

Good identifiers remain stable even when a visible title changes.

Queries#

A query asks the database to return selected information, summarize values, or make a controlled change. Filters narrow results, sorting controls order, and joins combine related records.

Data quality#

Validation rules prevent impossible or malformed values. Access control limits who can view or change information. Transactions group related changes so they succeed together or fail safely. Backups provide recovery after loss.

Database versus spreadsheet#

A spreadsheet is excellent for many personal and analytical tasks. A database becomes valuable when data has repeated structure, multiple relationships, concurrent users, strong validation needs, or application-driven queries.

Common mistakes#

A database is not automatically accurate; incorrect input and weak rules still produce unreliable results. It is also not simply “a file with rows.” The software manages structure, retrieval, relationships, and controlled updates.

Final model#

Think in entities, attributes, identifiers, relationships, validation rules, and the questions the system needs to answer.