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Development Tools Database Foundations Joining Relational Data Between Tables in SQL Keys and Auto-Incrementing Values

Elena Paraschiv
Elena Paraschiv
9,938 Points

Unique key_ can or cannot be NULL?

In the video Andrew says in the beginning that unique keys can be null , unless otherwise specified. And then later when he gives the example he says that they cannot be null. Imgur


So how is it like?

1 Answer

Roy Penrod
Roy Penrod
19,810 Points

Only one row in the database may have a null unique key. The reason is the unique key is used to ensure that no two rows have the same data in them.

Here's an answer from Stack Overflow that could help clear up the difference between a primary key and a unique key.