DA0-002 Data Concepts and Environments Practice Question
A data analyst is performing a join between two tables: 'employees' and 'departments'. The 'employees' table has a foreign key 'dept_id' referencing the 'departments' table. Which two join types would include all rows from the 'employees' table, regardless of whether there is a matching department? (Select TWO)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
LEFT JOIN
LEFT JOIN and RIGHT JOIN (if reversed) can include all rows from the left table. Specifically, LEFT JOIN includes all rows from the left table. FULL OUTER JOIN also includes all rows from both tables, but the question says 'all rows from the employees table' – that is satisfied by LEFT JOIN and also by FULL OUTER JOIN (which includes all from employees). However, the correct answer set: LEFT JOIN and FULL OUTER JOIN. The question says 'include all rows from the employees table' – RIGHT JOIN does not guarantee that unless employees is on the right side. So the correct two are LEFT JOIN and FULL OUTER JOIN.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
LEFT JOIN
Why this is correct
LEFT JOIN returns all rows from the left (employees) table.
- ✗
INNER JOIN
Why it's wrong here
INNER JOIN returns only rows with matching keys in both tables.
- ✗
CROSS JOIN
Why it's wrong here
CROSS JOIN creates a Cartesian product, not a conditional join.
- ✗
RIGHT JOIN
Why it's wrong here
RIGHT JOIN returns all rows from the right table; employees would need to be on the right.
- ✓
FULL OUTER JOIN
Why this is correct
FULL OUTER JOIN returns all rows from both tables, including all employees.
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