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CMA Intermediate · Financial Management and Business Data Analytics · Data Processing, Organisation, Cleaning and Validation

Two tables are to be integrated: a customer master with 500 unique customer IDs and a transactions table with 2,000 rows, each carrying one customer ID that exists in the master. If transactions are joined to the master using a left join on customer ID, with customer ID unique in the master, how many rows will the result contain?

The result will contain 2,000 rows. A left join retains every transaction row, and since each customer ID appears only once in the master, every transaction matches exactly one customer record, so no rows are added or duplicated by the join.

  1. A2,000Correct
  2. B500
  3. C2,500
  4. D1,000,000

Explanation

A left join keeps every row of the left table (transactions). Because customer ID is unique in the master, each transaction matches exactly one master row, so no duplication occurs. The result has 2,000 rows. 2,500 wrongly adds the tables, and 1,000,000 is a cross-product error.

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