# Distinct

DISTINCT

PostgreSQL-dagi DISTINCT kalit so’zi SELECT bayonotining natijalar to'plamidan dublikatlarni olib tashlash uchun ishlatiladi. U SELECT roʻyxatidagi barcha ustunlarni taqqoslaydi va barcha ustunlarda bir xil qiymatga ega boʻlgan qatorlarni yoʻq qiladi.

SYNTAX:

```sql
SELECT DISTINCT column1, column2
FROM table_name;
```

Bu kodning natijasidan table\_name ya’ni bu siz bergan table dan ichidagi ikkita column distinct qilib qaytaradi ya’ni dublikatlarni (bir necha marta qaytarilgan qiymatlarni) yo'qotadi.

Misol: Keling, quyidagi ma'lumotlarga ega "xodimlar" nomli jadvalni ko'rib chiqaylik:

| id | name  | salary |
| -- | ----- | ------ |
| 1  | John  | 50000  |
| 2  | Jack  | 55000  |
| 3  | John  | 60000  |
| 4  | Emily | 65000  |
| 5  | Jack  | 70000  |

"Xodimlar" jadvalidan (distinct) nomlar ro'yxatini olish uchun biz quyidagi so'rovdan foydalanishimiz mumkin:

```sql
SELECT DISTINCT name FROM employees;
```

Natija:

```
|name|  
-----
| John |
| Jack |
| Emily |
```

Xulosa qilib aytganda, PostgreSQL-dagi DISTINCT kalit so'zi jadvaldan qaytarilmas qiymatlarni olish uchun foydali vositadir. U bir yoki bir nechta ustunlar bilan ishlatilishi mumkin va natija to'plamidan dublikatlarni olib tashlaydi. Biroq, undan oqilona foydalanish kerak, chunki u katta ma'lumotlar to'plamlari bilan foydalanilganda so'rovlar ishlash tezligiga ta'sir qilishi mumkin.


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