Question

Explain Null and unique key​

Answer 1

Answer:

In other words, the index that is automatically created when you define a UNIQUE constraint will guarantee that no two rows in that table can have the same value for the columns participating in that index, with the ability to insert only one unique NULL value to these columns, if the column allows NULL.

Answer 2

Null : means having no value in the other words null is zero

Unique key : a unique key is a set of more than one feilds of a table that uniquely identify a record in database table

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