1. Question 1

Query that returns employees belonging to the department with the highest department ID:

• ❌ Query 1

• ❌ Query 2

• ✅ SELECT * FROM EMPLOYEES WHERE DEP_ID = ( SELECT MAX(DEPT_ID_DEP) FROM DEPARTMENTS )

• ❌ Query 4

Explanation:

MAX(DEPT_ID_DEP) gives the highest department ID, and the subquery returns that value.

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2. Question 2

Correct way to join EMPLOYEES and DEPARTMENTS:

• ❌ Query 1 (incorrect column names)

• ❌ Query 2

• ❌ Query 3 (uses implicit join but ambiguous columns)

• ✅ SELECT E.F_NAME, D.DEP_NAME FROM EMPLOYEES E, DEPARTMENTS D WHERE E.DEP_ID = D.DEPT_ID_DEP

Explanation:

You must join E.DEP_ID with D.DEPT_ID_DEP, selecting employee name and department name.

(Note: Query 4 has no join condition → Cartesian product. Incorrect.)

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3. Question 3

Correct query for total cost with alias Total_Cost:

• ❌ SELECT SUM(Cost)

• ✅ SELECT SUM(Cost) AS Total_Cost FROM PetRescue

• ❌ SUM(Total_Cost)

• ❌ SELECT Total_Cost

Explanation:

AS Total_Cost renames the output column.

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4. Question 4

Correct query to compute total days lived:

• ❌ SELECT (CURRENT_DATE – DOB)

• ✅ SELECT DATEDIFF(CURRENT_DATE, DOB) FROM Employees

• ❌ FROM_DAYS(DATEDIFF()) gives years, not days lived

• ❌ Incorrect syntax

Explanation:

DATEDIFF(date1, date2) returns the number of days between two dates.

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5. Question 5

Correct query to compute DOE = DOM + 1 year:

• ❌ DATEADD (not MySQL)

• ❌ INTERVAL 1 YEARS (incorrect plural)

• ❌ DATEADD again incorrect

• ✅ SELECT NAME, DATE_ADD(DOM, INTERVAL 1 YEAR) AS DOE FROM MEDS

Explanation:

MySQL uses DATE_ADD(date, INTERVAL value unit).

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🧾 Summary Table

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