[Solved] What is the main difference between UNION and UNION ALL in PostgreSQL? — Ans: UNION removes duplicate rows, while UNION ALL keeps all rows including... | PostgreSQL

PostgreSQL - Set Operations and Advanced Queries

What is the main difference between UNION and UNION ALL in PostgreSQL?

A<code>UNION</code> removes duplicate rows, while <code>UNION ALL</code> keeps all rows including duplicates.

B<code>UNION</code> requires matching column names, <code>UNION ALL</code> does not.

C<code>UNION ALL</code> removes duplicates, <code>UNION</code> keeps duplicates.

D<code>UNION</code> can combine different numbers of columns, <code>UNION ALL</code> cannot.

Step-by-Step Solution

Solution:

Step 1: Understand the behavior of UNION
UNION combines results from two queries and removes duplicate rows to give unique results.
Step 2: Understand the behavior of UNION ALL
UNION ALL combines results but keeps all rows, including duplicates.
Final Answer:
UNION removes duplicates, UNION ALL keeps duplicates. -> Option A
Quick Check:
Duplicates removed = UNION, duplicates kept = UNION ALL [OK]

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

Common Mistakes:

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What is the main difference between UNION and UNION ALL in PostgreSQL?