Why UNION ALL with duplicates in SQL? - Purpose & Use Cases

The Big Idea

What if you could combine lists instantly without losing any details or making mistakes?

The Scenario

Imagine you have two lists of names on paper from two different events. You want to combine them into one big list. You try to write them all down by hand, but some names appear in both lists.

The Problem

Writing down every name manually is slow and tiring. You might accidentally skip some names or write duplicates without realizing. Checking for duplicates by hand is confusing and wastes time.

The Solution

Using UNION ALL in SQL lets you quickly combine two lists exactly as they are, including duplicates. It saves time and avoids mistakes by letting the computer do the work.

Before vs After

✗ Before

Copy list A names
Copy list B names
Paste all names in one list

✓ After

SELECT name FROM listA
UNION ALL
SELECT name FROM listB

What It Enables

You can instantly merge multiple data sets with all entries preserved, making it easy to analyze combined information.

Real Life Example

A company wants to see all customer orders from two different stores, including repeated customers who ordered at both places, to understand total sales volume.

Key Takeaways

Manually combining lists is slow and error-prone.

UNION ALL merges data quickly and keeps duplicates.

This helps analyze complete combined data without losing any entries.