lesson
A stable identifier separates similar records
1 · Learn
A table groups records with defined fields. A key identifies a record reliably even when display names match or change. Two books can share a title while having different catalogue identifiers.
Choose consistent field types and keep personal information out of practice data. A key's purpose is identity, not a guarantee that every other field is correct. Validate values separately.
2 · Worked example
I use invented book IDs B01 and B02 for two records with the same title. Editing one title should not silently change the other record.
3 · Your turn
Why is a person's name alone often a poor unique key?
Check your answer
Names can be shared or changed, so they do not reliably identify one distinct record.
4 · Apply your learning
Create an invented collection with unique IDs, then test duplicate names and a changed display label.
Adult guidance and safety
Use an approved private interpreter, simulator or authoring tool with fictional data. Trace and predict before running. Never execute unknown downloaded code, inspect real credentials or use other people's private data. Working examples still need saved-project and assessment integration before release.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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