D492 Data Analytics Applications - Set 5 - Part 3

Correct Answer: To return only the rows that match in both tables

The INNER JOIN returns only the rows that have matching values in both tables. It does not include unmatched rows, which are handled by LEFT JOIN or RIGHT JOIN.

Correct Answer: GROUP BY

The GROUP BY clause is used to group rows that have the same values in specified columns. It is often used with aggregate functions like SUM(), COUNT(), or AVG().

Correct Answer: To link rows between two tables based on related columns

A FOREIGN KEY creates a relationship between two tables by linking a column in one table to a primary key in another table. It helps enforce referential integrity between the tables.

Correct Answer: LIKE

The LIKE operator is used to return rows that match a specified pattern, often using wildcards such as % or _. It is commonly used for pattern matching in string columns.

Correct Answer: To filter groups after aggregation

The HAVING clause filters groups after aggregation, typically used with the GROUP BY clause. It is similar to the WHERE clause but specifically used for aggregated data.

Correct Answer: MAX()

The MAX() function returns the maximum value in a column. MIN() returns the minimum value, COUNT() returns the number of rows, and SUM() adds numeric values.

Correct Answer: To save changes made during a transaction

The COMMIT statement saves the changes made during a transaction to the database. If the changes need to be undone, the ROLLBACK statement is used.

Correct Answer: CURDATE()

The CURDATE() function returns the current date in SQL. NOW() returns both the current date and time, TIME() returns only the time, and YEAR() extracts the year from a date.

Correct Answer: Removes all rows from a table but keeps the table structure

The TRUNCATE statement removes all rows from a table, but the table structure remains intact. It is faster than DELETE because it does not log individual row deletions.

Correct Answer: IS NULL

The IS NULL operator is used to check if a value is NULL. IS NOT NULL checks for non-NULL values, while = NULL and != NULL are not valid for checking NULL values in SQL.