What are SQL joins, and what are the different types of joins?

 SQL joins are used to combine rows from two or more tables based on a related column between them. The result of a join is a new table that contains columns from the joined tables, with rows that satisfy the specified join condition. SQL joins are fundamental for retrieving data from multiple tables and are a core concept in relational databases.

There are several types of joins, including:

1. 
   

2. 1.INNER JOIN: An inner join returns only the rows that have matching values in both tables. Rows from one table that don't have a corresponding match in the other table are excluded from the result.

   SELECT columns
   FROM table1
   INNER JOIN table2 ON table1.column_name = table2.column_name;
   

3. 
   

4. 2.LEFT JOIN (or LEFT OUTER JOIN): A left join returns all rows from the left table (table1), and the matching rows from the right table (table2). If there is no match in the right table, NULL values are included in the result.

   SELECT columns
   FROM table1
   LEFT JOIN table2 ON table1.column_name = table2.column_name;
   

5. 
   

6. 3.RIGHT JOIN (or RIGHT OUTER JOIN): A right join is similar to a left join but returns all rows from the right table and the matching rows from the left table. Rows from the left table without a match in the right table result in NULL values.

   SELECT columns
   FROM table1
   RIGHT JOIN table2 ON table1.column_name = table2.column_name;
   

7. 
   

8. 4.FULL JOIN (or FULL OUTER JOIN): A full join returns all rows when there is a match in either the left or right table. If there's no match, NULL values are included for the non-matching side.

   SELECT columns
   FROM table1
   FULL JOIN table2 ON table1.column_name = table2.column_name;
   

9. 
   

10. 5.CROSS JOIN: A cross join (or Cartesian join) combines each row from the left table with each row from the right table, resulting in a Cartesian product of the two tables. It doesn't require a join condition.

    SELECT columns
    FROM table1
    CROSS JOIN table2;
    

11. 
    

12. 6.SELF JOIN: A self join is used to join a table with itself. It can be helpful when you have hierarchical data or need to compare rows within the same table.

    SELECT e1.name, e2.name
    FROM employees e1
    JOIN employees e2 ON e1.manager_id = e2.employee_id;
    

These are the primary types of SQL joins. The choice of which join to use depends on the specific data you want to retrieve and the relationships between the tables. Understanding how to use joins effectively is crucial for working with relational databases and retrieving meaningful information from multiple related tables.