Oracle Joins

Joins are one of the most important concepts in SQL databases, including Oracle. They allow us to combine data from multiple tables based on common columns. Oracle provides different types of joins, each with its own syntax and uses.

Types of Joins

Inner Join

An inner join returns only the matching rows from both tables by comparing the values of the specified columns.

SELECT t1.column1, t1.column2, t2.column3
FROM table1 t1
INNER JOIN table2 t2
ON t1.common_column = t2.common_column;

Left Join

A left join returns all the rows from the left table and matching rows from the right table. If there is no matching row in the right table, NULL values are returned for the right table columns.

SELECT t1.column1, t1.column2, t2.column3
FROM table1 t1
LEFT JOIN table2 t2
ON t1.common_column = t2.common_column;

Right Join

A right join returns all the rows from the right table and matching rows from the left table. If there is no matching row in the left table, NULL values are returned for the left table columns.

SELECT t1.column1, t1.column2, t2.column3
FROM table1 t1
RIGHT JOIN table2 t2
ON t1.common_column = t2.common_column;

Full Outer Join

A full outer join returns all the rows from both tables. If there is no matching row in the other table, NULL values are returned.

SELECT t1.column1, t1.column2, t2.column3
FROM table1 t1
FULL OUTER JOIN table2 t2
ON t1.common_column = t2.common_column;

Cross Join

A cross join returns the Cartesian product of both tables, meaning all possible combinations of rows between the two tables.

SELECT t1.column1, t1.column2, t2.column3
FROM table1 t1
CROSS JOIN table2 t2;

Conclusion

Joins are essential for working with complex data scenarios in Oracle databases. They allow us to combine data from multiple tables and create meaningful relationships. Understanding the different types of joins and their syntax can greatly improve your ability to work with Oracle SQL.