Understanding Joins in Databases

What is the primary purpose of an INNER JOIN in SQL?

• To include all rows from the left table and matching rows from the right table

• To return only the rows that have matching values in both tables

• To include all rows from the right table and matching rows from the left table

• To return all rows from both tables regardless of matches

Which type of join would you use to include all rows from the left table and only the matching rows from the right table?

• INNER JOIN

• LEFT JOIN

• RIGHT JOIN

• FULL OUTER JOIN

What is a FULL OUTER JOIN used for?

• To return only the rows that have matching values in both tables

• To include all rows from the left table and matching rows from the right table

• To include all rows from both tables and fill in NULLs for non-matching rows

• To include all rows from the right table and matching rows from the left table

How do joins optimize engineering workflows in database management?

• By duplicating data across multiple tables

• By merging relevant data from multiple tables to provide comprehensive insights

• By deleting unnecessary data from tables

• By creating new tables for every query

Which join type is typically used to find unmatched records between two tables?

• INNER JOIN

• LEFT JOIN

• RIGHT JOIN

• FULL OUTER JOIN

What is a self-join?

• A join that combines rows from the same table

• A join that combines rows from different tables

• A join that does not use any condition

• A join that returns duplicate rows

Which SQL syntax correctly performs a RIGHT JOIN?

• SELECT FROM table1 LEFT JOIN table2 ON table1.id = table2.id;

• SELECT FROM table1 INNER JOIN table2 ON table1.id = table2.id;

• SELECT FROM table1 FULL OUTER JOIN table2 ON table1.id = table2.id;

• SELECT FROM table1 RIGHT JOIN table2 ON table1.id = table2.id;

Why is it important to consider performance when using joins in large datasets?

• Joins can significantly slow down query execution time

• Joins always improve query performance

• Joins have no effect on performance

• Joins delete unnecessary rows from datasets

What is the main difference between a LEFT JOIN and a RIGHT JOIN?

• LEFT JOIN returns all rows from the left table; RIGHT JOIN returns all rows from the right table

• LEFT JOIN returns unmatched rows; RIGHT JOIN does not return unmatched rows

• LEFT JOIN returns all rows from the right table; RIGHT JOIN returns all rows from the left table

• LEFT JOIN and RIGHT JOIN function the same way

In which scenario would a CROSS JOIN be most appropriate?

• When you need to combine rows with matching values from two tables

• When you need to return all possible combinations of rows from two tables

• When you need to return unmatched rows from two tables

• When you need to filter rows from one table based on another table