Write Queries to Combine Tables Using Various Join Operations (inner, Left, Right, and So on) with Single or Multiple Keys, as Well as Set Operations Like Union and Union All, Including the Differences Between the Joins (inner, Left, Right, and So On). DATA-ANALYST-ASSOCIATE Practice Questions (Page 6)

Questions 26–28

1. 26foundation · easy

   Which join type returns all rows from both tables, with NULLs in columns from the table that lacks a match?

   • AFULL OUTER JOIN
   • BLEFT JOIN
   • CCROSS JOIN
   • DINNER JOIN
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2. 27foundation · easy

   What is the primary difference between UNION and UNION ALL?

   • AUNION removes duplicates; UNION ALL retains all rows.
   • BUNION ALL is used for joins; UNION is used for set operations.
   • CUNION sorts the result; UNION ALL does not.
   • DUNION ALL removes duplicates; UNION retains all rows.
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3. 28expert · hard

   A data analyst is troubleshooting a query that uses a LEFT JOIN between `customers` (left) and `orders` (right). The analyst expects the result to have the same number of rows as the `customers` table, but the result has more rows. What is the most likely explanation?

   • AThe join condition is incorrect, causing a Cartesian product.
   • BThe `orders` table has multiple orders for some customers.
   • CThe analyst should have used an INNER JOIN instead.
   • DThe `customers` table has duplicate customer_id values.
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