Solution:Step 1: Identify columns to selectWe want order_id from both tables.Step 2: Use UNION ALL to combine including duplicatesSELECT order_id FROM Orders UNION ALL SELECT order_id FROM Returns; correctly selects order_id from both tables and combines with UNION ALL.Step 3: Check other options fo

[Solved] You have two tables:Orders(order_id, customer_id)Returns(order_id, customer_id)Write a query to list all order_ids from both tables including duplicates using UNION ALL. Which query is correct? | SQL

SQL - Set Operations

You have two tables:
Orders(order_id, customer_id)
Returns(order_id, customer_id)
Write a query to list all order_ids from both tables including duplicates using UNION ALL. Which query is correct?

ASELECT order_id FROM Orders JOIN Returns ON order_id UNION ALL;

BSELECT order_id FROM Orders UNION SELECT order_id FROM Returns;

CSELECT order_id FROM Orders UNION ALL SELECT order_id FROM Returns;

DSELECT order_id FROM Orders UNION ALL SELECT customer_id FROM Returns;

Step-by-Step Solution

Solution:

Step 1: Identify columns to select
We want order_id from both tables.
Step 2: Use UNION ALL to combine including duplicates
SELECT order_id FROM Orders UNION ALL SELECT order_id FROM Returns; correctly selects order_id from both tables and combines with UNION ALL.
Step 3: Check other options for errors
A has invalid JOIN syntax, B uses UNION (removes duplicates), D mismatches columns (customer_id).
Final Answer:
SELECT order_id FROM Orders UNION ALL SELECT order_id FROM Returns; -> Option C
Quick Check:
Correct UNION ALL query = SELECT order_id FROM Orders UNION ALL SELECT order_id FROM Returns; [OK]

Quick Trick: UNION ALL combines same columns from both tables including duplicates [OK]

Common Mistakes:

MISTAKES

Using UNION instead of UNION ALL
Mismatching columns in SELECTs
Incorrect JOIN syntax

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More SQL Quizzes

You have two tables:

Step 1: Identify columns to select

Step 2: Use UNION ALL to combine including duplicates

Step 3: Check other options for errors

Final Answer:

Quick Check:

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