notes

Question 3

What is the goal of the lecture on SQL and Boolean Logic?

Answer 3

Understand Boolean Logic and SQL Querying, learn how logic gates, truth tables, and Venn diagrams apply to database queries, master SQL commands for data manipulation, querying, and management, and build a structured approach to writing SQL queries efficiently.

Question 4

Who developed Boolean Logic?

Answer 4

George Boole (1815-1864) developed Boolean Logic.

Question 5

What are the basic values in Boolean Logic?

Answer 5

True (1) and False (0).

Question 6

What are the logical operators in Boolean Logic?

Answer 6

AND, OR, NOT.

Question 7

What is a truth table?

Answer 7

A truth table helps evaluate logical expressions.

Question 8

What does the AND operator do in SQL?

Answer 8

Both conditions must be true.

Example: SELECT * FROM employees WHERE department = ‘HR’ AND salary > 50000;

Question 9

What does the OR operator do in SQL?

Answer 9

At least one condition must be true.

Example: SELECT * FROM employees WHERE department = ‘HR’ OR department = ‘IT’;

Question 10

What does the NOT operator do in SQL?

Answer 10

Negates a condition.

Example: SELECT * FROM employees WHERE NOT department = ‘HR’;

Question 11

How do Venn diagrams relate to SQL queries?

Answer 11

They represent intersection (AND, INNER JOIN), union (OR, UNION), and difference (NOT, MINUS).

Question 12

What is SQL used for?

Answer 12

Defining database structures (DDL), manipulating data (DML), querying data (DQL), and controlling access (DCL).

Question 13

What is the purpose of the SELECT statement in SQL?

Answer 13

The SELECT command retrieves data.

Example: SELECT first_name, last_name FROM employees;

Question 14

How do you filter data in SQL?

Answer 14

Using the WHERE clause.

Example: SELECT * FROM employees WHERE salary > 60000;

Question 15

How do you sort data in SQL?

Answer 15

Using the ORDER BY clause.

Example: SELECT * FROM employees ORDER BY salary DESC;

Question 16

How do you remove duplicates in SQL?

Answer 16

Using the DISTINCT keyword.

Example: SELECT DISTINCT department FROM employees;

Question 17

What is an INNER JOIN in SQL?

Answer 17

Returns matching records.

Example: SELECT orders.order_id, customers.customer_name FROM orders INNER JOIN customers ON orders.customer_id = customers.customer_id;

Question 18

What is a LEFT JOIN in SQL?

Answer 18

Returns all from the left, matching from the right.

Example: SELECT customers.customer_name, orders.order_id FROM customers LEFT JOIN orders ON customers.customer_id = orders.customer_id;

Question 19

What is the COUNT() function in SQL?

Answer 19

Counts rows.

Example: COUNT(*)

Question 20

What is the SUM() function in SQL?

Answer 20

Adds values.

Example: SUM(salary)

Question 21

What is the AVG() function in SQL?

Answer 21

Calculates average.

Example: AVG(salary)

Question 22

What is the purpose of the INSERT statement?

Answer 22

Inserts data into a table.

Example: INSERT INTO employees (first_name, last_name, salary) VALUES (‘John’, ‘Doe’, 60000);

Question 23

How do you update data in SQL?

Answer 23

Using the UPDATE statement.

Example: UPDATE employees SET salary = 70000 WHERE first_name = ‘John’;

Question 24

How do you delete data in SQL?

Answer 24

Using the DELETE statement.

Example: DELETE FROM employees WHERE department = ‘HR’;

Question 25

How do you create a table in SQL?

Answer 25

Using the CREATE TABLE statement. ## Footnote Example: CREATE TABLE employees (id INT PRIMARY KEY, name VARCHAR(50) NOT NULL, salary INT);

Question 26

How do you alter a table in SQL?

Answer 26

Using the ALTER TABLE statement. ## Footnote Example: ALTER TABLE employees ADD COLUMN age INT;

Question 27

How do you drop a table in SQL?

Answer 27

Using the DROP TABLE statement. ## Footnote Example: DROP TABLE employees;

Question 28

What is the purpose of creating an index in SQL?

Answer 28

Improves search speed. ## Footnote Example: CREATE INDEX idx_salary ON employees (salary);

Question 29

What is a view in SQL?

Answer 29

A virtual table based on the result set of a SELECT statement. ## Footnote Example: CREATE VIEW high_salary AS SELECT * FROM employees WHERE salary > 80000;

Question 30

What is a trigger in SQL?

Answer 30

A set of instructions that are executed in response to certain events on a table. ## Footnote Example: CREATE TRIGGER before_insert BEFORE INSERT ON employees FOR EACH ROW SET NEW.salary = 50000 WHERE NEW.salary IS NULL;