SQL Joins are used to retrieve data from multiple tables based on a related column that exists in both tables. This is particularly useful when data is normalized and spread across different tables, and you want to bring it together in a single query result.
SQL Joins Syntax
SELECT columns FROM table1 JOIN table2 ON table1.common_column = table2.common_column;
SQL Joins Different Types of Joins
- INNER JOIN – Returns only the rows that have matching values in both tables. If there is no match, the row won’t appear in the result.
- LEFT JOIN (LEFT OUTER JOIN) – Returns all rows from the left table and the matched rows from the right table.
- 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, the result is NULL for columns from the left table.
- FULL JOIN (FULL OUTER JOIN) – Returns all rows when there is a macth in either left or right table. If there’s no match, NULL is shown for non-matching columns from either table.
- SELF JOIN – Returns rows from the same table that are joined with itself, allowing for comparisons between different rows within that table.
SQL Joins Labs
