How do you join two tables in SQL?
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In SQL, joining two tables means combining rows from both tables based on a related column between them, usually a primary key in one table and a foreign key in the other. Joins allow you to query data across multiple tables as if they were a single dataset.
Types of Joins in SQL:
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INNER JOIN
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Returns rows that have matching values in both tables.
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Example use case: Fetching customers who have placed orders.
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LEFT JOIN (LEFT OUTER JOIN)
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Returns all rows from the left table and the matched rows from the right table.
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If there’s no match, it returns NULL for right table columns.
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Example: List all customers, even those without orders.
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RIGHT JOIN (RIGHT OUTER JOIN)
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Returns all rows from the right table and the matched rows from the left table.
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If there’s no match, it returns NULL for left table columns.
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Example: List all orders, including those that might not yet be linked to customers.
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FULL JOIN (FULL OUTER JOIN)
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Returns rows when there’s a match in either left or right table.
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If no match exists, NULL values are filled in for the missing side.
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Example: Combine all customers and all orders, showing matches where possible.
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CROSS JOIN
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Returns the Cartesian product of the two tables (all combinations of rows).
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Rarely used, except for generating test datasets or special scenarios.
INNER JOIN
-
Returns rows that have matching values in both tables.
-
Example use case: Fetching customers who have placed orders.
LEFT JOIN (LEFT OUTER JOIN)
-
Returns all rows from the left table and the matched rows from the right table.
-
If there’s no match, it returns
NULLfor right table columns. -
Example: List all customers, even those without orders.
RIGHT JOIN (RIGHT OUTER JOIN)
-
Returns all rows from the right table and the matched rows from the left table.
-
If there’s no match, it returns
NULLfor left table columns. -
Example: List all orders, including those that might not yet be linked to customers.
FULL JOIN (FULL OUTER JOIN)
-
Returns rows when there’s a match in either left or right table.
-
If no match exists,
NULLvalues are filled in for the missing side. -
Example: Combine all customers and all orders, showing matches where possible.
CROSS JOIN
-
Returns the Cartesian product of the two tables (all combinations of rows).
-
Rarely used, except for generating test datasets or special scenarios.
✅ In short:
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Joins combine related data across tables.
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INNER JOIN → common records only.
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LEFT/RIGHT JOIN → all from one table + matching from the other.
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FULL JOIN → all records from both tables.
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CROSS JOIN → all possible combinations.
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