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Question 1 of 60 Quiz ID: 1

Which SQL standard was the first to be formally adopted by ANSI and ISO?

SQL-86

SQL-89

SQL-92

SQL:1999

Question 2 of 60 Quiz ID: 2

What is the key difference between CHAR(n) and VARCHAR(n) data types?

CHAR(n) has variable length while VARCHAR(n) has fixed length

CHAR(n) has fixed length while VARCHAR(n) has variable length

CHAR(n) supports Unicode while VARCHAR(n) does not

CHAR(n) is for numbers while VARCHAR(n) is for text

Question 3 of 60 Quiz ID: 3

What happens when you declare an attribute as PRIMARY KEY in a CREATE TABLE statement?

It automatically becomes NOT NULL and UNIQUE

It automatically becomes FOREIGN KEY

It allows NULL values by default

It creates an index but allows duplicates

Question 4 of 60 Quiz ID: 4

What is the difference between DROP TABLE and DELETE FROM statements?

DROP TABLE deletes content and structure, DELETE FROM only deletes content

DELETE FROM deletes content and structure, DROP TABLE only deletes content

Both statements perform identical operations

DROP TABLE is for temporary tables, DELETE FROM is for permanent tables

Question 5 of 60 Quiz ID: 5

In the basic SQL query structure SELECT A1, A2 FROM r1, r2 WHERE P, what does the WHERE clause correspond to in relational algebra?

Projection operation

Selection operation

Cartesian product operation

Join operation

Question 6 of 60 Quiz ID: 6

When would you use the DISTINCT keyword in a SELECT clause?

To select only unique column names

To eliminate duplicate tuples from the query result

To make the query case-sensitive

To select only distinct data types

Question 7 of 60 Quiz ID: 7

What does the asterisk (*) represent in a SELECT clause?

It selects only primary key columns

It selects all attributes from the specified relations

It performs multiplication operations

It indicates a required parameter

Question 8 of 60 Quiz ID: 8

In the FROM clause, what operation does listing multiple relations correspond to in relational algebra?

Selection

Projection

Cartesian product

Natural join

Question 9 of 60 Quiz ID: 9

What is the primary purpose of the WHERE clause in an SQL query?

To specify which tables to query

To define the output format

To specify conditions that result tuples must satisfy

To order the result set

Question 10 of 60 Quiz ID: 10

What is the main risk when using NATURAL JOIN?

It requires more memory than other joins

It can incorrectly equate unrelated attributes with the same name

It only works with numeric data types

It doesn't support foreign key relationships

Question 11 of 60 Quiz ID: 11

What is the purpose of the AS clause in SQL?

To create new tables

To rename relations or attributes in the query result

To specify aggregate functions

To define subqueries

Question 12 of 60 Quiz ID: 12

How does the ORDER BY clause sort results by default?

Descending order

Random order

Ascending order

By primary key order

Question 13 of 60 Quiz ID: 13

What does the LIKE operator with pattern '%dar%' match?

Exactly 'dar'

Any string starting with 'dar'

Any string containing 'dar' as a substring

Any string ending with 'dar'

Question 14 of 60 Quiz ID: 14

What is the purpose of the BETWEEN operator in SQL?

To compare two tables

To check if a value is within a specified range

To perform string pattern matching

To join tables based on range conditions

Question 15 of 60 Quiz ID: 15

Which aggregate function calculates the average value of a numeric column?

SUM()

AVG()

COUNT()

MAX()

Question 16 of 60 Quiz ID: 16

What does COUNT(*) aggregate function do?

Counts only distinct values

Counts all tuples, including those with NULL values

Counts only non-NULL values

Counts only primary key values

Question 17 of 60 Quiz ID: 17

When must attributes appear in the GROUP BY clause?

When they are used in aggregate functions

When they are mentioned in the SELECT clause outside of aggregate functions

When they are foreign keys

When they have NULL values

Question 18 of 60 Quiz ID: 18

What is the key difference between WHERE and HAVING clauses?

WHERE is for grouping, HAVING is for filtering

WHERE filters rows before grouping, HAVING filters groups after grouping

HAVING is used with aggregate functions, WHERE is not

WHERE is for joins, HAVING is for subqueries

Question 19 of 60 Quiz ID: 19

How do aggregate functions typically handle NULL values?

They treat NULL as zero

They include NULL in calculations

They ignore NULL values in the aggregated column

They convert NULL to empty strings

Question 20 of 60 Quiz ID: 20

What is a nested subquery in SQL?

A query that uses multiple FROM clauses

A select-from-where expression nested within another query

A query that references itself

A query with multiple SELECT statements

Question 21 of 60 Quiz ID: 21

Which SQL data type would be most appropriate for storing a product price with exactly 2 decimal places?

INT

REAL

NUMERIC(p,d)

VARCHAR(n)

Question 22 of 60 Quiz ID: 22

What is the practical difference between DROP TABLE and ALTER TABLE DROP?

DROP TABLE removes the entire table, ALTER TABLE DROP removes only a column

ALTER TABLE DROP removes the entire table, DROP TABLE removes only a column

Both perform identical operations but with different syntax

DROP TABLE is faster but less secure

Question 23 of 60 Quiz ID: 23

In a practical scenario, when would you use SELECT DISTINCT?

When you want to see all possible values including duplicates

When you need to eliminate duplicate rows from your result set

When you're selecting from multiple tables

When you're using aggregate functions

Question 24 of 60 Quiz ID: 24

Why might you use arithmetic expressions in the SELECT clause?

To perform calculations on retrieved data

To create new tables

To filter query results

To join multiple tables

Question 25 of 60 Quiz ID: 25

In a real-world database, why would you use table aliases with the AS clause?

To shorten long table names in queries involving multiple joins

To change the actual table names in the database

To improve database performance

To encrypt table names

Question 26 of 60 Quiz ID: 26

When would you use the ORDER BY clause in a practical application?

To alphabetize customer names in a report

To filter out unwanted records

To calculate totals and averages

To create new database tables

Question 27 of 60 Quiz ID: 27

In what practical situation would you use the LIKE operator with pattern matching?

To find customers with names containing 'smith'

To calculate average sales figures

To join customer and order tables

To create backup copies of tables

Question 28 of 60 Quiz ID: 28

Why would you use the BETWEEN operator instead of multiple AND conditions?

It makes range queries more readable and concise

It executes faster than equivalent AND conditions

It works with string data while AND doesn't

It automatically excludes NULL values

Question 29 of 60 Quiz ID: 29

In a sales database, which aggregate function would you use to find the total revenue?

AVG()

SUM()

COUNT()

MAX()

Question 30 of 60 Quiz ID: 30

When would you use GROUP BY in a practical business scenario?

To calculate total sales by product category

To alphabetize a customer list

To find a specific customer record

To update product prices

Question 31 of 60 Quiz ID: 31

In what scenario would you use HAVING instead of WHERE?

When filtering groups based on aggregate values

When filtering individual rows before grouping

When joining multiple tables

When creating new tables

Question 32 of 60 Quiz ID: 32

Why might you use nested subqueries in a real application?

To find customers who placed orders in the last month

To update all prices in a single operation

To create backup copies of tables

To improve database performance

Question 33 of 60 Quiz ID: 33

What is a practical use of foreign key constraints?

To prevent orphan records and maintain referential integrity

To improve query performance

To encrypt database relationships

To automatically backup related tables

Question 34 of 60 Quiz ID: 34

In a customer orders database, which query would find customers from 'Moratuwa'?

SELECT * FROM customers WHERE city = 'Moratuwa'

SELECT * FROM orders WHERE city = 'Moratuwa'

UPDATE customers SET city = 'Moratuwa'

DELETE FROM customers WHERE city != 'Moratuwa'

Question 35 of 60 Quiz ID: 35

How would you find employees who earn more than their department's average salary?

Using a subquery with AVG() in WHERE clause

Using ORDER BY with DESC

Using NATURAL JOIN without conditions

Using LIKE with pattern matching

Question 36 of 60 Quiz ID: 36

Which query would list projects with budgets over 1,000,000?

SELECT proj_name FROM project WHERE budget > 1000000

SELECT proj_name FROM project WHERE budget < 1000000

UPDATE project SET budget = 1000000

DELETE FROM project WHERE budget <= 1000000

Question 37 of 60 Quiz ID: 37

How would you find the number of employees in each city?

SELECT city, COUNT(*) FROM employee GROUP BY city

SELECT COUNT(*) FROM employee ORDER BY city

SELECT city FROM employee WHERE COUNT(*) > 0

UPDATE employee SET city = COUNT(*)

Question 38 of 60 Quiz ID: 38

What query would find the highest salary in each department?

SELECT dept, MAX(salary) FROM employee GROUP BY dept

SELECT dept, salary FROM employee ORDER BY salary DESC

SELECT MAX(salary) FROM employee WHERE dept IS NOT NULL

UPDATE employee SET salary = MAX(salary)

Question 39 of 60 Quiz ID: 39

How would you find employees who work on projects located in their home city?

Using a join between employee and project tables with city comparison

Using ORDER BY on city columns

Using AVG() aggregate function

Using LIKE with wildcard patterns

Question 40 of 60 Quiz ID: 40

Which query would update salaries by giving a 10% raise to all employees?

UPDATE employee SET salary = salary * 1.10

SELECT salary * 1.10 FROM employee

DELETE FROM employee WHERE salary = salary * 1.10

INSERT INTO employee VALUES (salary * 1.10)

Question 41 of 60 Quiz ID: 41

How would you find the total hours worked on each project?

SELECT proj_no, SUM(hours) FROM assignment GROUP BY proj_no

SELECT proj_no, hours FROM assignment ORDER BY hours

SELECT SUM(hours) FROM assignment WHERE proj_no IS NOT NULL

UPDATE assignment SET hours = SUM(hours)

Question 42 of 60 Quiz ID: 42

What is the practical purpose of the NOT NULL constraint?

To ensure critical data is always provided

To make queries run faster

To allow duplicate values

To create automatic backups

Question 43 of 60 Quiz ID: 43

In an e-commerce database, how would you find products that have never been ordered?

Using a subquery with NOT IN

Using ORDER BY with ASC

Using NATURAL JOIN without conditions

Using AVG() aggregate function

Question 44 of 60 Quiz ID: 44

Which SQL operation would you use to combine customer names with their order dates?

JOIN between customers and orders tables

UNION of customers and orders tables

GROUP BY on customer_id

UPDATE customers SET order_date

Question 45 of 60 Quiz ID: 45

How would you find the most expensive product in each category?

Using GROUP BY with MAX() and a subquery or window function

Using ORDER BY with LIMIT 1

Using LIKE with pattern matching

Using UPDATE with MAX()

Question 46 of 60 Quiz ID: 46

What is a practical use of the DISTINCT keyword with COUNT()?

To count unique values in a column

To make the count faster

To count all values including duplicates

To ignore NULL values automatically

Question 47 of 60 Quiz ID: 47

How would you find employees who have the same salary as their manager?

Using self-join with salary comparison

Using GROUP BY with AVG()

Using ORDER BY with DESC

Using LIKE with exact match

Question 48 of 60 Quiz ID: 48

Which query would delete all orders older than 5 years?

DELETE FROM orders WHERE order_date < CURRENT_DATE - INTERVAL '5 years'

SELECT * FROM orders WHERE order_date < 5

UPDATE orders SET order_date = NULL WHERE order_date IS OLD

DROP TABLE orders WHERE order_date < 5

Question 49 of 60 Quiz ID: 49

How would you find the average order value for each customer?

SELECT customer_id, AVG(order_total) FROM orders GROUP BY customer_id

SELECT AVG(order_total) FROM orders ORDER BY customer_id

SELECT customer_id FROM orders WHERE AVG(order_total) > 0

UPDATE orders SET order_total = AVG(order_total)

Question 50 of 60 Quiz ID: 50

What is the practical purpose of using transactions with SQL statements?

To ensure multiple operations succeed or fail together

To make individual queries run faster

To automatically create table backups

To simplify SQL syntax

Question 51 of 60 Quiz ID: 51

How would you find products that are priced above the average price of all products?

Using a subquery with AVG() in WHERE clause

Using GROUP BY with HAVING

Using NATURAL JOIN without conditions

Using ORDER BY with DESC LIMIT 1

Question 52 of 60 Quiz ID: 52

Which SQL feature would you use to ensure email addresses are unique across users?

UNIQUE constraint on email column

PRIMARY KEY on email column

FOREIGN KEY referencing another table

LIKE with pattern matching

Question 53 of 60 Quiz ID: 53

How would you find the top 3 highest-paid employees?

SELECT name, salary FROM employee ORDER BY salary DESC LIMIT 3

SELECT MAX(salary) FROM employee GROUP BY name LIMIT 3

SELECT name, salary FROM employee WHERE salary = TOP3

UPDATE employee SET salary = TOP3

Question 54 of 60 Quiz ID: 54

What is a practical use of the COALESCE function?

To replace NULL values with default values

To calculate averages ignoring zeros

To concatenate strings with spaces

To convert numbers to strings

Question 55 of 60 Quiz ID: 55

How would you update product prices by applying a 15% discount to discontinued items?

UPDATE products SET price = price * 0.85 WHERE discontinued = true

SELECT price * 0.85 FROM products WHERE discontinued

DELETE FROM products WHERE price = price * 0.85

INSERT INTO products VALUES (price * 0.85)

Question 56 of 60 Quiz ID: 56

Which query would find customers who have placed more than 5 orders?

SELECT customer_id FROM orders GROUP BY customer_id HAVING COUNT(*) > 5

SELECT customer_id FROM orders WHERE COUNT(*) > 5

SELECT customer_id FROM orders ORDER BY COUNT(*) DESC

UPDATE orders SET customer_id = 5 WHERE COUNT(*) > 5

Question 57 of 60 Quiz ID: 57

How would you calculate the total sales for the current month?

SELECT SUM(amount) FROM sales WHERE EXTRACT(MONTH FROM sale_date) = EXTRACT(MONTH FROM CURRENT_DATE)

SELECT SUM(amount) FROM sales WHERE sale_date = THIS_MONTH

SELECT amount FROM sales ORDER BY sale_date DESC

UPDATE sales SET amount = SUM(amount)

Question 58 of 60 Quiz ID: 58

What is the practical purpose of database indexes?

To speed up query performance on frequently searched columns

To store backup copies of table data

To encrypt sensitive column data

To automatically update related tables

Question 59 of 60 Quiz ID: 59

How would you find employees who were hired in the last 30 days?

SELECT name FROM employees WHERE hire_date >= CURRENT_DATE - INTERVAL '30 days'

SELECT name FROM employees WHERE hire_date < 30

SELECT name FROM employees ORDER BY hire_date DESC LIMIT 30

UPDATE employees SET hire_date = CURRENT_DATE - 30

Question 60 of 60 Quiz ID: 60

Why would you use SQL views in a practical application?

To simplify complex queries and provide a security layer

To make physical copies of tables for backup

To improve database storage efficiency

To automatically optimize query performance

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