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DATE

Ushbu o'quv qo'llanma PostgreSQL DATE ma'lumotlar turini muhokama qiladi va sana qiymatlarini boshqarish uchun ba'zi qulay sana funktsiyalaridan qanday foydalanishni ko'rsatadi.

PostgreSQL sana ma'lumotlarini saqlash imkonini beruvchi DATE turini taklif etadi.

PostgreSQL sana qiymatini saqlash uchun 4 baytdan foydalanadi. DATE maʼlumotlar turining eng past va eng yuqori qiymatlari miloddan avvalgi 4713 va 5874897 milodiy.

Agar siz DATE ustuniga ega jadval yaratsangiz va PostgreSQL serverining joriy sanasidan standart qiymat sifatida foydalanmoqchi bo'lsangiz, DEFAULT kalit so'zidan keyin CURRENT_DATE ko'rsatkichidan foydalanishingiz mumkin.

Misol uchun, quyidagi bayonot DATE ma'lumotlar turi bilan posting_date ustuniga ega bo'lgan documents jadvalini yaratadi.

CREATE TABLE documents (
  document_id serial PRIMARY KEY, 
  header_text VARCHAR (255) NOT NULL, 
  posting_date DATE NOT NULL DEFAULT CURRENT_DATE
);

posting_date ustuni joriy sanani standart qiymat sifatida qabul qiladi. Bu shuni anglatadiki, agar siz yangi qator kiritishda qiymat ko'rsatmasangiz, PostgreSQL joriy sanani posting_date ustuniga kiritadi. Masalan:

INSERT INTO documents (header_text) 
VALUES ('Billing to customer XYZ')
RETURNING *;
document_id |       header_text       | posting_date
-------------+-------------------------+--------------
           1 | Billing to customer XYZ | 2024-02-01
(1 row)

E'tibor bering, ma'lumotlar bazasi serveringizning joriy sanasiga qarab siz boshqa e'lon qilingan sana qiymatini olishingiz mumkin.

PostgreSQL DATE funktsiyalari

Namoyish uchun biz employee_id, first_name, last_name, birth_date va hire_date ustunlaridan iborat yangi employees jadvalini yaratamiz, bu erda birth_date va hire_date ustunlarining ma'lumotlar turlari DATE bo'ladi.

CREATE TABLE employees (
  employee_id SERIAL PRIMARY KEY, 
  first_name VARCHAR (255) NOT NULL, 
  last_name VARCHAR (255) NOT NULL, 
  birth_date DATE NOT NULL, 
  hire_date DATE NOT NULL
);

INSERT INTO employees (first_name, last_name, birth_date, hire_date)
VALUES ('Shannon','Freeman','1980-01-01','2005-01-01'),
       ('Sheila','Wells','1978-02-05','2003-01-01'),
       ('Ethel','Webb','1975-01-01','2001-01-01')
RETURNING *;

Chiqish:

 employee_id | first_name | last_name | birth_date | hire_date
-------------+------------+-----------+------------+------------
           1 | Shannon    | Freeman   | 1980-01-01 | 2005-01-01
           2 | Sheila     | Wells     | 1978-02-05 | 2003-01-01
           3 | Ethel      | Webb      | 1975-01-01 | 2001-01-01
(3 rows)


INSERT 0 3

1. Hozirgi sana

Joriy sana va vaqtni olish uchun siz o'rnatilgan NOW() funksiyasidan foydalanasiz:

SELECT NOW();

Chiqish:

              now
-------------------------------
 2024-02-01 08:48:09.599933+07
(1 row)

Faqat sana qismini (vaqt qismisiz) olish uchun siz DATETIME qiymatini DATE qiymatiga uzatish uchun cast operatoridan (::) foydalanasiz:

SELECT NOW()::date;

Chiqish:

    now
------------
 2024-02-01
(1 row)

Joriy sanani olishning tezkor usuli CURRENT_DATE funksiyasidan foydalanishdir:

SELECT CURRENT_DATE;

Chiqish:

 current_date
--------------
 2024-02-01
(1 row)

Natija yyyy-mm-dd formatida bo'ladi. Biroq, TO_CHAR() funksiyasidan foydalanib sana qiymatini formatlash orqali boshqa formatdan foydalanishingiz mumkin.

2. Muayyan formatda PostgreSQL sana qiymatini chiqaring

Muayyan formatda sana qiymatini chiqarish uchun siz TO_CHAR() funksiyasidan foydalanasiz.

TO_CHAR() funksiyasi ikkita parametrni qabul qiladi. Birinchi parametr formatlashni xohlagan qiymat, ikkinchisi esa chiqish formatini belgilaydigan shablondir.

Masalan, joriy sanani dd/mm/yyyy formatida ko'rsatish uchun siz quyidagi bayonotdan foydalanasiz:

SELECT TO_CHAR(CURRENT_DATE, 'dd/mm/yyyy');
  to_char
------------
 01/02/2024
(1 row)

Sanani Feb 01, 2024 kabi formatda ko'rsatish uchun siz quyidagi bayonotdan foydalanasiz:

SELECT TO_CHAR(CURRENT_DATE, 'Mon dd, yyyy');
   to_char
--------------
 Feb 01, 2024
(1 row)

3. Ikki sana orasidagi intervalni oling

Ikki sana orasidagi intervalni olish uchun siz minus (-) operatoridan foydalanasiz.

Quyidagi misolda bugungi kundan boshlab hire_date ustunidagi qiymatlarni ayirish orqali xodimlarning xizmat kunlari olinadi:

SELECT 
  first_name, 
  last_name, 
  now() - hire_date as diff 
FROM 
  employees;
 first_name | last_name |           diff
------------+-----------+---------------------------
 Shannon    | Freeman   | 6970 days 08:51:20.824847
 Sheila     | Wells     | 7701 days 08:51:20.824847
 Ethel      | Webb      | 8431 days 08:51:20.824847
(3 rows)

4. Yoshlarni yillar, oylar va kunlarda hisoblang

Joriy sanadagi yoshni yillar, oylar va kunlarda hisoblash uchun AGE() funksiyasidan foydalanasiz.

Quyidagi bayonot employees jadvalidagi xodimlarning yoshini hisoblash uchun AGE() funksiyasidan foydalanadi.

SELECT
	employee_id,
	first_name,
	last_name,
	AGE(birth_date)
FROM
	employees;

Chiqish:

 employee_id | first_name | last_name |           age
-------------+------------+-----------+--------------------------
           1 | Shannon    | Freeman   | 44 years 1 mon
           2 | Sheila     | Wells     | 45 years 11 mons 24 days
           3 | Ethel      | Webb      | 49 years 1 mon
(3 rows)

Agar siz AGE() funksiyasiga sana qiymatini o'tkazsangiz, u ushbu sana qiymatini joriy sanadan olib tashlaydi.

Agar siz AGE() funksiyasiga ikkita argumentni uzatsangiz, u birinchi argumentdan ikkinchi argumentni olib tashlaydi.

Masalan, 01/01/2015 yildagi xodimlarning yoshini olish uchun siz quyidagi bayonotdan foydalanasiz:

SELECT 
  employee_id, 
  first_name, 
  last_name, 
  age('2015-01-01', birth_date) 
FROM 
  employees;

Chiqish:

 employee_id | first_name | last_name |           age
-------------+------------+-----------+--------------------------
           1 | Shannon    | Freeman   | 35 years
           2 | Sheila     | Wells     | 36 years 10 mons 24 days
           3 | Ethel      | Webb      | 40 years
(3 rows)

5. Sana qiymatidan yil, chorak, oy, hafta va kunni ajratib oling

Sana qiymatidan yil, chorak, oy, hafta va kunni olish uchun siz EXTRACT() funksiyasidan foydalanasiz.

Quyidagi bayonotda xodimlarning tug'ilgan sanasidan yil, oy va kun ko'rsatilgan:

SELECT
	employee_id,
	first_name,
	last_name,
	EXTRACT (YEAR FROM birth_date) AS YEAR,
	EXTRACT (MONTH FROM birth_date) AS MONTH,
	EXTRACT (DAY FROM birth_date) AS DAY
FROM
	employees;

Chiqish:

 employee_id | first_name | last_name | year | month | day
-------------+------------+-----------+------+-------+-----
           1 | Shannon    | Freeman   | 1980 |     1 |   1
           2 | Sheila     | Wells     | 1978 |     2 |   5
           3 | Ethel      | Webb      | 1975 |     1 |   1
(3 rows)

Ushbu qo'llanmada siz PostgreSQL DATE ma'lumotlar turi va sana ma'lumotlarini qayta ishlash uchun ba'zi qulay funktsiyalar haqida bilib oldingiz.

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