Objective 2.3 Merge and Load Data Sets CERTIFIED-DATA-SCIENCE-PRACTITIONER Practice Questions (Page 1)

Questions 1–5

1. 1expert · hard

   A data scientist has two tables: `transactions` (transaction_id, customer_id, amount, date) and `customer_feedback` (feedback_id, customer_id, rating, date). The scientist needs a dataset with all transactions and any matching feedback, but only for customers who have at least one transaction. Which join is correct?

   • AInner join transactions with customer_feedback on customer_id
   • BLeft join transactions with customer_feedback on customer_id
   • CRight join transactions with customer_feedback on customer_id
   • DFull outer join transactions with customer_feedback on customer_id
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2. 2foundation · easy

   Which Python framework is commonly used to create a lightweight REST API endpoint to serve a cleaned dataset?

   • APandas
   • BNumPy
   • CDjango
   • DFlask
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4. 3foundation · easy

   You are merging a customer table with a transaction table on `customer_id`. The customer table has unique `customer_id` values, but the transaction table has multiple rows per customer. What type of join will this produce?

   • AOne-to-one join
   • BCartesian join
   • CMany-to-many join
   • DOne-to-many join
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5. 4expert · hard

   A database administrator needs to load a large CSV into a PostgreSQL table that has a foreign key constraint to a parent table. Some rows in the CSV reference non-existent parent keys. The load must succeed, and the bad rows must be identified. What is the best approach?

   • ALoad the data with COPY and let it fail, then fix the source file
   • BLoad into a staging table without the FK constraint, then insert valid rows and report invalid ones
   • CUse INSERT ... ON CONFLICT DO NOTHING
   • DDisable the FK constraint, load the data, then re-enable it
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6. 5foundation · easy

   Why is it important to ensure that a join key is unique in at least one of the datasets before performing a many-to-one merge?

   • ATo speed up the merge operation
   • BTo allow the merge to use an outer join
   • CTo avoid creating duplicate rows in the result
   • DTo ensure the key column is sorted
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