lesson
A query asks for a defined subset
1 · Learn
A query selects records meeting conditions and can choose which fields to return. In a simple SQL example, SELECT title FROM courses WHERE year = 10 asks for titles of records whose year equals 10. The result depends on the stored data.
Filtering a display is not deleting the excluded rows. For applications, use parameterised queries rather than constructing executable query text from untrusted input.
2 · Worked example
A year-10 filter leaves year-9 records stored even when they are not shown in the result.
3 · Your turn
Does hiding year-9 rows with a WHERE year = 10 query delete them?
Check your answer
No. It selects a subset for the result without deleting other rows.
4 · Apply your learning
Predict results from a small supplied table and compare with a read-only query in an approved sandbox.
Adult guidance and safety
Work in an approved local sandbox with invented records and test accounts. Do not access other people's systems or collect real credentials. Practical project evidence is required in addition to these explanations; this is not a specified GCSE Computer Science course.
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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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