CREATE TABLE Project (
  pno INTEGER PRIMARY KEY,
  pname VARCHAR,
  ptype VARCHAR,
  duration INTEGER
);

CREATE TABLE Employee (
  eno INTEGER PRIMARY KEY,
  ename VARCHAR,
  qualification VARCHAR,
  joining_date DATE
);

CREATE TABLE Project_Employee(
  pno INTEGER REFERENCES Project(pno),
  eno INTEGER REFERENCES Employee(eno),
  start_date_of_project DATE,
  no_of_hours_worked INTEGER
);

INSERT INTO Project VALUES(11,'Robotics','AI',49);
INSERT INTO Project VALUES(12,'Machine','Robot',80);
INSERT INTO Project VALUES(13,'Super Computer','Tech',96);
INSERT INTO Project VALUES(14,'Mainframe Computer','Tech',57);

INSERT INTO Employee VALUES(111,'Akshay','IT','11/2/2020');
INSERT INTO Employee VALUES(112,'Vijay','MCA','9/5/2019');
INSERT INTO Employee VALUES(113,'Akash','MSC Computer','2/5/2020');
INSERT INTO Employee VALUES(114,'Yash','IT','1/30/2020');

INSERT INTO Project_Employee VALUES(11,111,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(11,112,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(11,113,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(11,114,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(12,111,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(12,112,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(12,113,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(12,114,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(13,111,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(13,112,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(13,113,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(13,114,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(14,111,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(14,112,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(14,113,'12/23/2020',56);
INSERT INTO Project_Employee VALUES(14,114,'12/23/2020',56);

SELECT * FROM Project;
SELECT * FROM Employee;
SELECT * FROM Project_Employee;


/*
Q1. Write a trigger before inserting the duration into the project
table and make sure that the duration is always greater than zero.
Display appropriate message 
*/

CREATE OR REPLACE FUNCTION Check_Duration()
RETURNS TRIGGER AS'
DECLARE
BEGIN
IF NEW.duration <= 0 THEN
RAISE NOTICE ''Duration is Always Greater than Zero.'';
END IF;
RETURN NULL;
END;'
language'plpgsql';

CREATE TRIGGER T1 BEFORE INSERT ON Project FOR EACH ROW EXECUTE PROCEDURE Check_Duration();
/*
DROP TRIGGER IF EXISTS T1 ON Project;

insert into Project VALUES (15,'Jarvis','AI',0);

SELECT * FROM Project;
*/


/*
Q2. Write a function using cursor to accept project name as input
parameter and display names of employees working on it
*/

CREATE OR REPLACE FUNCTION PrintEmp(name text)
RETURNS INTEGER AS '
DECLARE 

c1 CURSOR for select ename,qualification from employee where eno 
IN(select eno from Project_Employee where pno 
IN(select pno from project where pname = name));

empname text;
qual text;

BEGIN
open c1;

loop 
fetch c1 into empname,qual;
EXIT WHEN NOT FOUND;
raise notice ''% %'',empname,qual;
end loop;
close c1;
RETURN 1;
END;'
language 'plpgsql';

select PrintEmp('Robotics');

PostgreSQL online editor

Write, Run & Share PostgreSQL queries online using OneCompiler's PostgreSQL online editor and compiler for free. It's one of the robust, feature-rich online editor and compiler for PostgreSQL. Getting started with the OneCompiler's PostgreSQL editor is really simple and pretty fast. The editor shows sample boilerplate code when you choose database as 'PostgreSQL' and start writing queries to learn and test online without worrying about tedious process of installation.

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;