Solution:Step 1: List rows from both tablesTable A has ids 1, 2, 3; Table B has ids 2, 3, 4.Step 2: Apply UNION behaviorUNION combines all rows and removes duplicates, so final list is 1, 2, 3, 4.Final Answer:[1, 2, 3, 4] -> Option AQuick Check:UNION removes duplicates = [1, 2, 3, 4] [OK]

[Solved] Given two tables:Table A: id123Table B: id234What is the result of:SELECT id FROM A UNION SELECT id FROM B; | SQL

SQL - Set Operations

Given two tables:

Table A: id
1
2
3

Table B: id
2
3
4

What is the result of:
SELECT id FROM A UNION SELECT id FROM B;

A[1, 2, 3, 4]

B[1, 2, 2, 3, 3, 4]

C[2, 3]

D[1, 4]

Step-by-Step Solution

Solution:

Step 1: List rows from both tables
Table A has ids 1, 2, 3; Table B has ids 2, 3, 4.
Step 2: Apply UNION behavior
UNION combines all rows and removes duplicates, so final list is 1, 2, 3, 4.
Final Answer:
[1, 2, 3, 4] -> Option A
Quick Check:
UNION removes duplicates = [1, 2, 3, 4] [OK]

Quick Trick: UNION removes duplicates, so no repeated ids appear [OK]

Common Mistakes:

MISTAKES

Expecting duplicates to appear
Confusing UNION with UNION ALL
Listing only common ids

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Given two tables:

Step 1: List rows from both tables

Step 2: Apply UNION behavior

Final Answer:

Quick Check:

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