IS NULL value allowed in unique key?

Question

Yes you can have Null value in a unique key but only if all the columns are NULL. If you have created index on more than 1 column them if the other key is NOT NULL then you will get error.

Can we store null value in unique key column?

The primary key column cannot have null values while the Unique Key column can have one null value.

How many NULL values can be stored in a unique key column?

As you know, when you create a UNIQUE constraint on a nullable column, SQL Server allows only one NULL value, thereby maintaining the UNIQUEness. However, there are situations when we need more than one NULL value in the column but still have to maintain uniqueness, ignoring all those NULL values.

Expert · Answer

The primary key column cannot have null values while the Unique Key column can have one null value.

Expert · Answer

As you know, when you create a UNIQUE constraint on a nullable column, SQL Server allows only one NULL value, thereby maintaining the UNIQUEness. However, there are situations when we need more than one NULL value in the column but still have to maintain uniqueness, ignoring all those NULL values.

IS NULL value allowed in unique key?

Can we store null value in unique key column?

How many NULL values can be stored in a unique key column?

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