Solution:Step 1: Understand UNION ALL behaviorUNION ALL combines all rows from both queries including duplicates.Step 2: List all emp_id valuesEmployees has 101, 102, 103; Contractors has 102, 103, 104.Step 3: Combine resultsAll values appear in the result, duplicates included: 101, 102, 103, 102, 1

[Solved] Consider two tables:Employees: emp_id101102103Contractors: emp_id102103104What will be the output of:SELECT emp_id FROM Employees UNION ALL SELECT emp_id FROM Contractors; | SQL

SQL - Set Operations

Consider two tables:

Employees: emp_id
101
102
103

Contractors: emp_id
102
103
104

What will be the output of:
SELECT emp_id FROM Employees UNION ALL SELECT emp_id FROM Contractors;

A101, 102, 103, 104

B101, 102, 103, 102, 103, 104

C102, 103, 104

D101, 102, 103

Step-by-Step Solution

Solution:

Step 1: Understand UNION ALL behavior
UNION ALL combines all rows from both queries including duplicates.
Step 2: List all emp_id values
Employees has 101, 102, 103; Contractors has 102, 103, 104.
Step 3: Combine results
All values appear in the result, duplicates included: 101, 102, 103, 102, 103, 104.
Final Answer:
101, 102, 103, 102, 103, 104 -> Option B
Quick Check:
Duplicates are preserved in UNION ALL [OK]

Quick Trick: UNION ALL keeps duplicates; UNION removes them [OK]

Common Mistakes:

MISTAKES

Assuming duplicates are removed
Confusing UNION ALL with UNION
Listing only unique values

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More SQL Quizzes

Consider two tables:

Step 1: Understand UNION ALL behavior

Step 2: List all emp_id values

Step 3: Combine results

Final Answer:

Quick Check:

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