Explain the differences between LEFT JOIN and RIGHT JOIN in SQL and their consequences when joining tables.
sobes.tech AI
Answer from AI
LEFT JOIN and RIGHT JOIN are types of table joins in SQL, which differ in the direction of row inclusion:
-
LEFT JOIN returns all rows from the left (first) table and the matching rows from the right (second) table. If there is no match, the right table's fields will be filled with NULL.
-
RIGHT JOIN returns all rows from the right table and the matching rows from the left table. If there is no match, the left table's fields will be NULL.
Consequences:
- With LEFT JOIN, you keep all data from the left table, even if there are no matches.
- With RIGHT JOIN, you keep all data from the right table.
Example:
SELECT A.id, B.value
FROM A
LEFT JOIN B ON A.id = B.a_id;
It will return all records from A, with matching records from B or NULL if there are no matches.
If replaced with RIGHT JOIN, it will return all records from B, with matching records from A or NULL.
The choice depends on which table you want to consider as the main one during the join.