Set datestyle to german;

Create table staff (
id integer primary key,
last_name varchar(64) not null,
first_name varchar(64) not null,
second_name varchar(64),
sex char(1) not null
check (sex= 'м' or sex='ж'),
birthday date,
post varchar(128),
department varchar(128),
unique (post, department),
head_id integer references staff (id));


Create sequence staff_id_seq;
Insert into staff values
((select nextval('staff_id_seq')), 'Сталин', 'Иосиф', 'Виссарионович', 'м', '21.12.1879', 'Председатель', 'ГКО', null),
((select nextval('staff_id_seq')), 'Молотов', 'Вячеслав', 'Михайлович', 'м', '09.03.1890', 'Заместитель председателя', 'ГКО', (select currval('staff_id_seq'))-1),
((select nextval('staff_id_seq')), 'Маленков', 'Георгий', 'Максимилианович', 'м', '08.01.1902', 'Начальник', 'УК ЦК ВКП(б)', (select currval('staff_id_seq'))-1),
((select nextval('staff_id_seq')), 'Ворошилов', 'Климент', 'Ефремович', 'м', '04.02.1881', 'Председатель КО', 'СНК', (select currval('staff_id_seq'))-2),
((select nextval('staff_id_seq')), 'Микоян', 'Анастас', 'Иванович', 'м', '25.11.1895', 'Председатель', 'КП-ВС РККА', (select currval('staff_id_seq'))-3);


Select b.last_name, b.first_name, b.second_name, b.post, h.last_name "hLast_name",
h.first_name "hFirstt_name", h.second_name "hSecond_name", h.post "hPost" from staff b
left outer join staff h on h.head_id=b.id;

With s as
(select b.id boss, h.head_id sub from staff b
left outer join staff h on h.head_id=b.id)

Update staff set head_id=1 where id in (select boss from s where sub is null);


With s as
(select b.id boss, h.head_id sub from staff b
left outer join staff h on h.head_id=b.id)

Update staff set head_id=1 where id in (select boss from s where sub is null);


CREATE OR REPLACE PROCEDURE birthday_boys(month integer) as $$
DECLARE
attr_e record;
a integer;
BEGIN
a:=0;
FOR attr_e in (SELECT * FROM staff where extract(month from birthday) = month)
LOOP
raise info '% % % ',attr_e.last_name,attr_e.first_name,attr_e.second_name;
a := a+1;
END LOOP;
raise info '%',a;
raise info '%', (SELECT max(extract(year from age(NOW(),birthday))) from staff where extract(month from birthday) = month);
raise info '%', (SELECT min(extract(year from age(NOW(),birthday))) from staff where extract(month from birthday) = month);
raise info '%', (SELECT round(avg(extract(year from age(NOW(),birthday))),0) from staff where extract(month from birthday) = month);
END
$$
LANGUAGE plpgsql;
call birthday_boys(12);

WITH RECURSIVE chain (id, head_id, len) AS(
SELECT id, head_id, 1
FROM staff WHERE head_id is null
UNION ALL
SELECT staff.id, staff.head_id, chain.len + 1
FROM chain
JOIN staff ON chain.id=staff.head_id)

SELECT max(len) FROM chain;

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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;