The words, without the shrug

One query for the list, then one per item.

Fetching 50 posts and then fetching each post’s author separately: 51 round trips. Invisible with test data, ruinous with real data. A database call inside a loop is the tell.

See also Query, Index

The same input can produce different output.

True of language models and untrue of most other APIs. Means tests cannot assert on exact strings, and that a bug may not reproduce on demand.

See also Hallucination, Streaming

Storing each fact in exactly one place.

Structuring tables so a customer email lives once and everything else points at it. Changing it is then one edit rather than a thousand. Deliberately duplicating for read speed is denormalisation, and you own keeping the copies in step.

See also Foreign key, Join

Databases that are not table-and-row relational.

A loose family including document, key-value and graph stores. Flexible shape and easier extreme scale, at the cost that nothing prevents two records disagreeing about structure. The schema does not disappear; it moves into your code.

See also SQL, Document store, Schema