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En Taze Makaleler
Ana Sayfa / Makaleler / Anahtar Mantığı Nedir ? Türleri Nelerdir ?
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Anahtar Mantığı Nedir ? Türleri Nelerdir ?

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handan-erdag-31-sql-keyBir kayıt içerisinde farklılıkları ve nitelikleri gösteren belirleyicilere anahtarlar (keys) denir. Bir tablo içerisinde bulunabilecek anahtarlar şunlardır :

  • Birincil anahtar (Primary key – PK)
  • Tekil anahtar (Unique key – UK)
  • Referans anahtar (Foreign key – FK)
  • Birleşik anahtardır (Composite key – CK)

Birincil Anahtar (Primary Key):
Bir tablo içerisindeki satırları birbirinden ayırt eder. Birincil anahtar olan bir veri aynı tablo içerisinde tekrarlanamaz. Yine bu alandaki veri boş bırakılamaz, yani NULL değeri alamaz. Tek bir alan birincil anahtar olabileceği gibi bazı tablolarda birden fazla alanın birleşmesiyle birincil anahtar oluşabilir.

Tekil Anahtar (Unique Key):
Tablonun tekil anahtar olarak tanımlanmış bir alanına aynı değer sadece bir kez girilebilir. Birincil anahtardan farklı olarak, tabloda bu alana ait sadece bir kayıt NULL değeri alabilir. Birincil anahtar aynı zamanda tek anahtar olarak sayılabilir fakat tek anahtarlar birincil anahtar değildirler.

Referans Anahtar (Foreign Key):
Tablodaki bir veriyi başka tablodaki bir veri ile ilişkilendirir. İki tablo arasında yapılan bu ilişkilendirme ile referans anahtar olarak tanımlanmış alana sadece ilişkilendirdiği tablonun alanındaki veriler eklenebilir.

Birleşik Anahtar (Composite Key):
Birden fazla alanın birleştirilmesiyle birincil anahtar görevini üstlenecek tanımlamalar yapılabilir. Bunlar birleşik anahtar olarak adlandırılır.

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Sevgili Okuyucu, bak bu makalede ilgini çekebilir.

Çok Da Fifi Hatunlar Stand Up

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