Mastering SQL Joins

What is the purpose of a JOIN in SQL?

• To combine rows from two or more tables based on a related column.

• To update existing records in a table.

• To create a new table in the database.

• To delete rows from a table.

What type of JOIN returns all records from the left table and matched records from the right table?

• RIGHT JOIN

• INNER JOIN

• LEFT JOIN

• FULL OUTER JOIN

Which SQL JOIN returns all records from both tables, regardless of whether there is a match?

• RIGHT JOIN

• FULL OUTER JOIN

• LEFT JOIN

• INNER JOIN

What is the difference between INNER JOIN and OUTER JOIN?

• OUTER JOIN only returns unmatched rows.

• INNER JOIN can include NULL values from both tables.

• INNER JOIN returns all rows from both tables.

• INNER JOIN returns matched rows; OUTER JOIN returns all rows from one table with matched rows from the other.

How do you perform a LEFT JOIN in SQL?

• SELECT columns FROM table1 LEFT JOIN table2 ON table1.common_column = table2.common_column;

• SELECT columns FROM table1 RIGHT JOIN table2 ON table1.common_column = table2.common_column;

• SELECT columns FROM table1 JOIN table2 USING (common_column);

• SELECT columns FROM table1 INNER JOIN table2 ON table1.common_column = table2.common_column;

What keyword is used to specify the condition for a JOIN?

• FILTER

• ON

• WITH

• WHERE

What does a CROSS JOIN do in SQL?

• A CROSS JOIN creates a new table with unique rows from both tables.

• A CROSS JOIN only combines rows with matching values.

• A CROSS JOIN filters rows based on a condition.

• A CROSS JOIN combines every row of one table with every row of another table.

Can you join more than two tables in a single SQL query?

• Joining more than two tables is not supported in SQL.

• Yes, you can join more than two tables in a single SQL query.

• You can only join tables if they have a common column.

• No, you can only join two tables at a time.

What is a self JOIN?

• A self JOIN is a type of JOIN that only retrieves unique records.

• A self JOIN is a JOIN operation between two different tables.

• A self JOIN is a JOIN operation that combines data from multiple databases.

• A self JOIN is a JOIN operation where a table is joined with itself.

What is the result of a RIGHT JOIN when there are no matches in the left table?

• No records returned from either table.

• Only the matching records from both tables.

• All records from the left table with NULLs for the right table columns.

• All records from the right table with NULLs for the left table columns.