union.md

📚 UNION

The UNION operator is used in SQL to combine the result sets of two or more SELECT statements.
It removes duplicate rows between the combined result sets by default.

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🛠️ Basic Syntax

SELECT column1, column2, ...
FROM table1
WHERE condition

UNION

SELECT column1, column2, ...
FROM table2
WHERE condition;

• Each SELECT statement must have the same number of columns.
• Columns must have compatible data types and appear in the same order.

Example

SELECT first_name, last_name
FROM employees
WHERE department = 'Sales'

UNION

SELECT first_name, last_name
FROM employees
WHERE department = 'Marketing';

• This query returns a combined list of employees from the Sales and Marketing departments, without duplicates.

Key Points

• UNION removes duplicate rows by default.
• If you want to include duplicates, use UNION ALL.
• The column names in the final result come from the first SELECT statement.

Additional Example

SELECT city
FROM customers

UNION

SELECT city
FROM suppliers;

• This query returns a distinct list of cities from both customers and suppliers.

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🎥 Video Notes

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📝 Problem Description

Describe the problem, challenge, or topic discussed in a video related to SELECT FROM.
What concept was explained or what exercise was solved?

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DataBase Given

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💻 My SQL Code

-- Write your SQL code attempt or solution related to SQL COMMAND
SQL COMMAND

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🧠 Solution Code / Explanation

SQL COMMAND

Explanation - Explain what you learned, any key takeaways, or how you solved the problem related to COMMAND._

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