Ushbu qo'llanmada siz ustun qiymatlari null bo'lmasligini ta'minlash uchun PostgreSQL-ning null bo'lmagan cheklovlari haqida bilib olasiz. Maʼlumotlar bazasi dunyosida NULL notanish yoki etishmayotgan ...

--It is for making record unique. --It does not accept "null" as value. --It does not accept "repeated data", all data in primary key field must be unique. --A table can have just a single "primary ...