SQL Test 3

What is the difference between primary key and unique key?

How do different data types handle NULL values?

What happens when you use UPDATE command without WHERE clause?

How does GROUP BY work with multiple columns?

From a customers table (customer_id, first_name, last_name, email, phone), find all customers whose email ends with '@gmail.com' and phone number is not NULL, showing only first_name and email.

What is a composite index and when should it be used?

What are the standard wildcard characters used with LIKE operator?

What is required in INNER JOIN syntax?

How does RIGHT JOIN work in SQL?

From an orders table (order_id, customer_id, order_date, total_amount), find the earliest order date, latest order date, lowest order amount, and highest order amount for each customer.

Which query returns student names in ascending order?

What is ENUM data type and when should it be used?

Insert a new employee (id=101, name='John Doe', dept='IT', salary=75000) into employees table, then update all IT employees' salaries by 10% increase.

Can HAVING clause be used without GROUP BY?

What does SELECT DISTINCT do?

How are indexes maintained when table data changes?

From a customers table (customer_id, first_name, last_name, email, phone), find customers whose first name starts with 'J', email contains 'gmail', and phone number ends with '123'.

You have three tables: orders (order_id, customer_id, product_id), customers (customer_id, name), and products (product_id, product_name). You want to list all orders with the customer name and product name for each order.

You have two tables listing projects: assigned_projects (project_id, project_name, owner) and completed_projects (project_id, completion_date). You need a complete list of all projects, showing their completion date if they are finished, and their owner if they are assigned. Some projects might be assigned but not finished, and others might be finished but not in the assigned list (e.g., historical projects).

Which aggregate function calculates the average salary of employees?