Constraint table in database

Hal yang sepele tapi kadang membingungkan….. mungkin seperti hal tentang constrain tabel ini…. bagi yang belum kenal mungkin bingung arti dari kata itu apa,,tapi sebenarnya kita sering menggunakannya,. berikut ini sekilas penjelasan tentang constrain…. semoga bermanfaat…

Constraint adalah batasan atau aturan yang ada pada table. Constraint mencegah penghapusan data dari suatu table yang mempunyai keterkaitan dengan table yang lain.

Macam-macam constraint :

  • NOT NULL :

Suatu kolom yang didefinisikan dengan constraint NOT NULL tidak boleh berisi nilai NULL.

  • UNIQUE :

Constraint UNIQUE mendefinisikan suatu kolom menjadi bersifat unik.

  • PRIMARY KEY :

Constraint PRIMARY KEY membentuk key yang unik untuk suatu table.

  • FOREIGN KEY :

FOREIGN KEY constraint didefinisikan pada suatu kolom yang ada pada suatu table, dimana kolom tersebut juga dimiliki oleh table yang lain sebagai suatu PRIMARY KEY.

  • CHECK :

Constraint CHECK digunakan untuk mendefinisikan suatu kondisi yang harus dipenuhi oleh tiap baris data dalam table.

Untuk Menghapus constraint perintah yang dapat digunakan yaitu “DROP ” :

ALTER TABLE table

DROP CONSTRAINT type (column);

Untuk Mengaktifkan constraint perintah yang dapat digunakan yaitu “ENABLE” :

ALTER TABLE table

ENABLE CONSTRAINT type (column);

Untuk Mematikan constraint perintah yang dapat digunakan yaitu “DISABLE ” :

ALTER TABLE table

DISABLE CONSTRAINT type (column );

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12 thoughts on “Constraint table in database

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