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Joining Multiple Tables: SQL Techniques

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Joining multiple tables in SQL involves combining rows from two or more tables based on a related column between them. Here are some common techniques for joining tables: https://www.youtube.com/watch?v=y5EM-oXxDTA

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Joining Multiple Tables: SQL Techniques

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by richa3412

by richa3412

                                        
                                                  Joining multiple tables in SQL involves combining rows from two or more tables based on a related column between them. Here are some common techniques for joining tables:
 1. INNER JOIN
Combines rows from both tables where there is a match on the specified columns.
'''sql
SELECT 
FROM table1
INNER JOIN table2
ON table1.column = table2.column;
'''
 2. LEFT JOIN (or LEFT OUTER JOIN)
Returns all rows from the left table and the matched rows from the right table. If no match is found, 'NULL' values are returned for columns from the right table.
'''sql
SELECT 
FROM table1
LEFT JOIN table2
ON table1.column = table2.column;
'''
 3. RIGHT JOIN (or RIGHT OUTER JOIN)
Returns all rows from the right table and the matched rows from the left table. If no match is found, 'NULL' values are returned for columns from the left table.
'''sql
SELECT 
FROM table1
RIGHT JOIN table2
ON table1.column = table2.column;
'''
 4. FULL JOIN (or FULL OUTER JOIN)
Returns all rows when there is a match in one of the tables. Rows from both tables that do not match will also be returned, with 'NULL' values where there is no match.
'''sql
SELECT 
FROM table1
FULL JOIN table2
ON table1.column = table2.column;
'''
 5. CROSS JOIN
Returns the Cartesian product of both tables, meaning all possible combinations of rows. This join does not require a condition.
'''sql
SELECT 
FROM table1
CROSS JOIN table2;
'''
 6. SELF JOIN
A self join is a regular join but the table is joined with itself.
'''sql
SELECT A., B.
FROM table1 A
INNER JOIN table1 B
ON A.column = B.column;
'''
 7. JOIN with Multiple Conditions
You can join tables based on multiple conditions.
'''sql
SELECT 
FROM table1
INNER JOIN table2
ON table1.column1 = table2.column1
AND table1.column2 = table2.column2;
'''
 Best Practices:
- Use Aliases: For better readability, especially with multiple joins, use table aliases.
- Optimize Queries: Be cautious with 'CROSS JOIN' and ensure proper indexing to optimize performance.
If you have any specific scenarios or questions, feel free to ask!