CREATE TABLE students
(
sno integer primary key,
sname varchar(50),
sclass varchar(20),
saddr varchar(100)
);

INSERT INTO students VALUES (1, 'Amol', 'FYBCA','pune');
INSERT INTO students VALUES (2,'Archana', 'FYBCA','pune');
INSERT INTO students VALUES (3,'Kiran', 'FYBCA','pune');
INSERT INTO students VALUES (4,'Amar','SYBCA','pune');
INSERT INTO students VALUES (5,'Suresh','TYBCA','pune');

SELECT * FROM students;


create table teacher
(  
tno integer primary key,
tname varchar(20),
qualification varchar(15),
experience integer
);

INSERT into teacher values(1,'Kumar','PHD',10);
INSERT into teacher values(2,'Veena','MPHIL',16);
INSERT into teacher values(3,'Ketki','MCS',2);
INSERT into teacher values(4,'Manisha','MCA',5);
INSERT into teacher values(5,'Prakash','MCA',3);

select * from teacher;

create table students_teacher
(
sno integer references students(sno),
tno integer references teacher(tno),
subject char(30),
marks integer
);

insert into students_teacher values(5,1,'C',60);
insert into students_teacher values(4,1,'C++',75);
insert into students_teacher values(2,1,'C',80);
insert into students_teacher values(3,2,'DS',78);
insert into students_teacher values(4,3,'ADBMS',70);

select *from students_teacher;

 create or replace function tech_cnt(name text) returns int as'
 declare
 cnt integer;
 begin
 select into cnt count(*)
 from students a,teacher b,students_teacher c
 where tname= name
 and a.sno=c.sno
 and b.tno=c.tno;
 return cnt;
 end;
 'Language 'plpgsql';
 
 select tech_cnt('Kumar');
 select tech_cnt('Veena');

create or replace function sub_cnt(name text) returns int as'
declare
no integer;
cnt integer;
begin
select into cnt distinct count(tno)
from students_teacher
where subject= name
group by tno;
return cnt;
end;
'Language 'plpgsql';

select sub_cnt('DS');
select sub_cnt('c');

create or replace function sub_sum(name text) returns int as'
declare
cnt integer;
begin
select into cnt sum(marks)
from students a, teacher b, students_teacher c
where sname= name
and a.sno=c.sno
and b.tno=c.tno
group by c.sno;
return cnt;
end;
'Language 'plpgsql';
select sub_sum('Suresh');

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;