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📚 JOIN WITH MULTIPLE KEYS

A JOIN with multiple keys uses more than one column to match rows between two tables.
This is useful when a relationship between tables depends on a combination of columns rather than just one.

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🛠️ Basic Syntax

SELECT columns
FROM table1
JOIN table2
ON table1.column1 = table2.column1
AND table1.column2 = table2.column2;

• JOIN matches rows where both (or more) column conditions are satisfied.
• AND connects multiple key comparisons.

Example

SELECT orders.order_id, products.product_name
FROM orders
JOIN products
ON orders.product_id = products.product_id
AND orders.product_version = products.product_version;

• This query matches orders to products based on both product_id and product_version.

Key Points

• Useful when a composite key defines the relationship between tables.
• All join conditions must be true for a match to occur.
• You can add even more conditions if needed with additional ANDs.

Additional Example

SELECT enrollment.student_id, students.student_name
FROM enrollment
JOIN students
ON enrollment.student_id = students.student_id
AND enrollment.school_year = students.school_year;

• This query matches students based on both their ID and school year.

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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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