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Graded Quiz: Basic SQL :Databases and SQL for Data Science with Python (IBM Data Analyst Professional Certificate) Answers 2025

1. Question 1

Result of:

SELECT DISTINCT FIRSTNAME FROM INSTRUCTOR

  • ✅ LEON
    PAUL
    JOE

  • ❌ LEON, PAUL, LEON, JOE

  • ❌ Repeated names

  • ❌ Full names with last names

Explanation:

DISTINCT FIRSTNAME returns each unique FIRSTNAME once, without duplicates.

2. Question 2

SQL:

UPDATE INSTRUCTOR SET LASTNAME = 'Brewster' WHERE LASTNAME = 'Smith'

  • ❌ Changes Brewster → Smith

  • ❌ Updates all rows to Brewster

  • ❌ Updates all rows to Smith

  • ✅ Changes the last name of all instructors named ‘Smith’ to ‘Brewster.’

Explanation:

WHERE LASTNAME = 'Smith' filters only those rows.

3. Question 3

Effect of:

DELETE FROM table;

(no WHERE clause)

  • ❌ Error

  • ✅ Removes all entries, leaving an empty table

  • ❌ Deletes only first entry

  • ❌ Deletes the table

Explanation:

DELETE without WHERE = delete all rows, but table structure remains.

4. Question 4

Result of:

SELECT COUNT(DISTINCT FIRSTNAME) FROM INSTRUCTOR

  • ❌ Only the distinct names

  • ❌ Distinct names + count

  • ❌ Error

  • ✅ Number of unique FIRSTNAME entries

Explanation:

COUNT(DISTINCT column) gives how many unique values exist.

5. Question 5

Result of:

SELECT * FROM INSTRUCTOR WHERE LASTNAME='Smith' LIMIT 5

  • ❌ First 5 rows of whole table

  • ❌ Last 5 rows

  • ❌ Last 5 entries where LASTNAME=’Smith’

  • ✅ First 5 entries where LASTNAME = ‘Smith’

Explanation:

LIMIT 5 returns the first 5 matching rows.

🧾 Summary Table

Q Correct Answer Key Concept
1 LEON, PAUL, JOE DISTINCT returns unique values
2 Smith → Brewster UPDATE with WHERE
3 Table emptied, not deleted DELETE without WHERE
4 Count of unique FIRSTNAME COUNT(DISTINCT)
5 First 5 Smith rows LIMIT filtering