Interview Q&A / SQL & DBMS

1. What is the difference between INNER JOIN and LEFT JOIN?

   INNER JOIN returns only rows that have a match in both tables. LEFT JOIN returns every row from the left table, and fills the right table's columns with NULL when there is no match.

   BeginnerIn-depth2 min read
2. What is a CROSS JOIN and when would you use it?

   A CROSS JOIN pairs every row of one table with every row of the other, giving rows1 x rows2 results. It is useful for generating combinations, such as every size with every colour.

   BeginnerQuick answer1 min read
3. What is a self join and when do you need one?

   A self join joins a table to itself using two different aliases. It is used when rows relate to other rows in the same table, such as an employee and their manager.

   BeginnerQuick answer1 min read
4. What is the difference between LEFT JOIN and RIGHT JOIN?

   LEFT JOIN keeps every row of the left table and fills NULLs where the right has no match. RIGHT JOIN does the opposite. They are mirror images, and any RIGHT JOIN can be rewritten as a LEFT JOIN by swapping the tables.

   BeginnerQuick answer1 min read