What potential issue should be considered when using correlated subqueries?
They can lead to performance issues if not used carefully.
They cannot be used with aggregate functions.
They cannot return more than one column.
They require the use of the JOIN clause.
What does the asterisk (*) symbol represent when used in a SELECT statement?
A wildcard for searching data
A specific column name
A comment indicator
All columns
In which scenario would a subquery be a more suitable choice than a JOIN operation?
When you need to filter data based on a condition that involves a separate query.
When you need to update data in one table based on data from another table.
When you need to combine data from multiple tables based on a common column.
When you need to sort data from multiple tables based on a common column.
What is the result of SELECT NOW(); in SQL?
SELECT NOW();
Current date
Current time
Current date and time
An error message
Which SQL statement is used to add new rows into a table?
INSERT
ADD
CREATE
APPEND
By default, how does the 'ORDER BY' clause sort data?
Randomly
Alphabetically
In descending order
In ascending order
What is the purpose of a subquery in SQL?
To define a new aggregate function.
To retrieve data from a table that will be used in a larger query.
To modify data in multiple tables simultaneously.
To create a temporary table for intermediate results.
To modify existing data in a table, which SQL statement would you use?
UPDATE
MODIFY
CHANGE
ALTER
What is the difference between CURDATE() and NOW() in SQL?
CURDATE()
NOW()
CURDATE() returns the current date, NOW() returns the current time.
CURDATE() returns the current date, NOW() returns the current date and time.
They are interchangeable.
CURDATE() returns the current date and time, NOW() returns the current date.
You want to find customers who have placed orders in the last month. You have two tables: 'Customers' and 'Orders'. Which subquery type would be most efficient to achieve this?
IN Subquery
EXISTS Subquery
Any of the above would be equally efficient.
Correlated Subquery