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MySQL UNION and UNION ALL

? MySQL UNION and UNION ALL

? Quick Overview

The UNION and UNION ALL operators in MySQL combine results from multiple SELECT queries into a single result set.

? Key Concepts

  • UNION removes duplicate rows.
  • UNION ALL keeps all rows including duplicates.

? Syntax / Theory

? View Code Example 
-- Combine two SELECT queries
SELECT column1, column2
FROM table1
UNION ALL
SELECT column1, column2
FROM table2;

? Code Example

? View Code Example 
-- Merge customer and supplier names
SELECT customer_name
FROM customers
UNION
SELECT supplier_name
FROM suppliers;

? Live Output / Explanation

The result combines rows from both tables into a single list.

? Interactive Idea

Try switching between UNION and UNION ALL to observe duplicate handling.

? Use Cases

  • Merging data from similar tables
  • Generating unified reports
  • Cross-table searches

✅ Tips & Best Practices

  • Use UNION ALL for better performance when duplicates are not a concern.
  • Ensure column count and data types match.

? Try It Yourself

  • Create a UNION query combining three tables.
  • Compare performance of UNION vs UNION ALL.