SQL Joins
SQL Joins
In SQL, a JOIN operation is used to combine rows from two or more tables based on a related column between them. Joining tables is one of the most powerful features of SQL, as it allows data from multiple tables to be combined into a single result set. Here are some types of JOIN operations:
- INNER JOIN:
An INNER JOIN returns only the rows that have matching values in both tables.
SELECT *
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;
- LEFT JOIN:
A LEFT JOIN returns all the rows from the left table and matching rows from the right table. If there are no matching rows in the right table, NULL values will be returned.
SELECT *
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;
- RIGHT JOIN:
A RIGHT JOIN returns all the rows from the right table and matching rows from the left table. If there are no matching rows in the left table, NULL values will be returned.
SELECT *
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name;
- FULL OUTER JOIN:
A FULL OUTER JOIN returns all the rows from both tables, including rows where there are no matches in either table. If there are no matches in one of the tables, NULL values will be returned.
SELECT *
FROM table1
FULL OUTER JOIN table2
ON table1.column_name = table2.column_name;
- CROSS JOIN:
A CROSS JOIN returns the Cartesian product of the two tables, meaning it returns all possible combinations of rows from both tables.
SELECT *
FROM table1
CROSS JOIN table2;
Overall, JOIN operations are a powerful tool in SQL that allow you to combine data from multiple tables in a single result set. By understanding the different types of JOINs available, you can write more complex queries that extract the information you need from your database.