Module 09 Knowledge Check
5 questions. Pass mark 4 out of 5. Answer every question before checking the answer key below, then retry after reading the feedback.
1. LIKE '%delhi%' fails to match 'Delhi' in a case-sensitive database. The robust fix is…
- A. Add more wildcards
- B. Normalise case on both sides, e.g. LOWER(column) LIKE LOWER(pattern)
- C. Use = instead
- D. Use BETWEEN
2. The main risk of free-text categories like city names is…
- A. They use storage
- B. Spelling and spacing variants split one real category into many
- C. They cannot be indexed
- D. They are always NULL
3. A CASE expression that buckets values should always include…
- A. An index hint
- B. An ELSE branch so unmatched values are visible rather than silently NULL
- C. A LIMIT
- D. A window function
4. Trimming whitespace before grouping matters because…
- A. It looks neater
- B. 'Delhi ' and 'Delhi' are different values and form separate groups
- C. It speeds up joins
- D. It removes NULLs
5. When preparing text columns as features for later analysis, you should record…
- A. Nothing
- B. The normalisation rules applied, so results are reproducible and reviewable
- C. Only the row count
- D. The database version
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Answer Key and Explanations
Check these only after attempting every question.
1. B - Normalise case on both sides, e.g. LOWER(column) LIKE LOWER(pattern)
Explicit normalisation makes matching behaviour independent of engine collation settings.
2. B - Spelling and spacing variants split one real category into many
'New Delhi', 'new delhi', and 'New Delhi' become three groups in a GROUP BY.
3. B - An ELSE branch so unmatched values are visible rather than silently NULL
Without ELSE, anything unexpected becomes NULL and disappears from your categories.
4. B - 'Delhi ' and 'Delhi' are different values and form separate groups
Invisible characters are a leading cause of duplicated categories.
5. B - The normalisation rules applied, so results are reproducible and reviewable
Undocumented cleaning cannot be reproduced or challenged, which breaks the evidence trail.
Practical Check
Apply this module to your own work: complete the module activity for *Text Fields, Categorisation, and Feature Preparation*, then write one sentence naming what your result shows and one naming what it does not.
Strong Answer Pattern
A strong answer names the task, the evidence used, the check performed, and the remaining limitation. It avoids "proved", "guaranteed", or "always" unless the evidence genuinely supports it.