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📚 SELF JOIN

A SELF JOIN is a SQL operation where a table is joined with itself.
It is useful for comparing rows within the same table.

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🛠️ Basic Syntax

SELECT A.column1, B.column2
FROM table_name A
JOIN table_name B
ON A.common_column = B.common_column;

• You create table aliases (A, B) to differentiate between the two instances of the same table.
• The ON clause specifies how the rows are matched.

Example

SELECT A.employee_id, A.first_name, B.manager_id, B.first_name AS manager_name
FROM employees A
JOIN employees B
ON A.manager_id = B.employee_id;

• This query lists employees along with the names of their managers.

Key Points

• A SELF JOIN requires table aliases to avoid confusion.
• It behaves like a regular join but matches rows within the same table.
• Useful for hierarchical or relationship-based data (like employees and managers).

Additional Example

SELECT A.customer_name AS referrer, B.customer_name AS referred
FROM customers A
JOIN customers B
ON A.customer_id = B.referrer_id;

• This query shows customers and the customers they referred.

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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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