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sql_joins

🗂 SQL Joins Cheatsheet

Join Type	Keeps Rows From	When To Use	Example Use Case
INNER JOIN ✅	Matching rows in both tables	When you only need rows that exist in both tables	Get users who have orders
LEFT JOIN	All rows from left + matches from right	When you need all left rows, even if no match on right	List all users + their orders (NULL if none)
RIGHT JOIN	All rows from right + matches from left	Rarely used; same as LEFT JOIN but reversed	List all orders + user info (NULL if user deleted)
FULL OUTER JOIN	All rows from both tables	When you want everything, matched or not	Combine active + archived users
CROSS JOIN	Cartesian product (all combinations)	For generating combinations or test data	Pair every product with every store
SELF JOIN	Table joins itself	Compare rows within the same table	Find employees who report to the same manager

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