Could you explain the working principle of anti join and how it differs from other types of joins in databases?

Anti join is a type of join that returns rows from the first table for which there are no matching rows in the second table. In simpler terms, it shows records that have no matches.

In SQL, anti join is usually implemented using a LEFT JOIN and checking for NULL in the columns of the second table, or using NOT EXISTS or NOT IN.

Differences from other types of joins:

• INNER JOIN returns only matching records from both tables.
• LEFT JOIN returns all records from the left table and matching ones from the right, if any.
• Anti join returns only those records from the left table for which there are no matches in the right.

Example in SQL:

SELECT a.*
FROM tableA a
LEFT JOIN tableB b ON a.id = b.a_id
WHERE b.a_id IS NULL;

This query will return all records from tableA for which there are no corresponding records in tableB.