-- Create Students table
CREATE TABLE Students (
    StudentID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Email VARCHAR(100),
    Year INT
);


-- Insert sample data into Students table
INSERT INTO Students (StudentID, FirstName, LastName, Email, Year) VALUES
(1, 'John', 'Doe', '[email protected]', 2),
(2, 'Jane', 'Smith', '[email protected]', 1),
(3, 'Mike', 'Brown', '[email protected]', 3),
(4, 'Emily', 'Wilson', '[email protected]', 1),
(5, 'David', 'Johnson', '[email protected]', 1),
(6, 'Anna', 'Martinez', '[email protected]', 2),
(7, 'Carlos', 'Garcia', '[email protected]', 1),
(8, 'Sara', 'Lee', '[email protected]', 2),
(9, 'Alex', 'Wilson', '[email protected]', 3),
(10, 'Nina', 'Patel', '[email protected]', 4),
(11, 'Omar', 'Khan', '[email protected]', 1),
(12, 'Tara', 'Sharma', '[email protected]', 2),
(13, 'Liam', 'Wilson', '[email protected]', 2),
(14, 'Ava', 'Patel', '[email protected]', 1),
(15, 'Ethan', 'Sharma', '[email protected]', 3),
(16, 'Mia', 'Wilson', '[email protected]', 4),
(17, 'Aryan', 'Patel', '[email protected]', 2),
(18, 'Isha', 'Sharma', '[email protected]', 1);


-- questions
-- List all students whose ID is larger than 5
-- List all students whose FirstName starts with 'A'
-- Add one year for all students/Reduce one year from all students
-- What's the average year of all students?
-- How many students do we have for each year?
-- What's the average year for the students for each unique family name (with more than one students having that family name)?
select avg(year) from students group by LastName having count(*) > 1;
by

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About PostgreSQL

PostgreSQL is a open source relational database system and is also knows as Postgres.

Key Features:

  • Postgres is not only free and open-source but also it is highly extensible.
  • Custom Data types and funtions from various programming languaues can be introduced and the good part is compiling entire database is not required.
  • ACID(Atomicity, Consistency, Isolation, Durability) compliant.
  • First DBMS which implemented Multi-version concurrency control (MVCC) feature.
  • It's the default database server for MacOS.
  • It supports all major operating systems like Linux, Windows, OpenBSD,FreeBSD etc.

Syntax help

1. CREATE

CREATE command is used to create a table, schema or an index.

Syntax:

         CREATE TABLE table_name (
                column1 datatype,
                column2 datatype,
                ....);

2. ALTER

ALTER command is used to add, modify or delete columns or constraints from the database table.

Syntax

ALTER TABLE Table_name ADD column_name datatype;

3. TRUNCATE:

TRUNCATE command is used to delete the data present in the table but this will not delete the table.

Syntax

TRUNCATE table table_name;

4. DROP

DROP command is used to delete the table along with its data.

Syntax

DROP TABLE table_name;

5. RENAME

RENAME command is used to rename the table name.

Syntax

ALTER TABLE table_name1 RENAME to new_table_name1;

6. INSERT

INSERT Statement is used to insert new records into the database table.

Syntax

INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);

7. SELECT

Select statement is used to select data from database tables.

Syntax:

SELECT column1, column2, ...
FROM table_name;

8. UPDATE

UPDATE statement is used to modify the existing values of records present in the database table.

Syntax

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

9. DELETE

DELETE statement is used to delete the existing records present in the database table.

Syntax

DELETE FROM table_name where condition;