Can a NULL field be unique?

Question

You can insert NULL values into columns with the UNIQUE constraint because NULL is the absence of a value, so it is never equal to other NULL values and not considered a duplicate value.

Can a unique field be NULL MySQL?

A unique key can contain a NULL value where each NULL value is itself unique (that is, NULL != NULL). Likewise, the million_words table contains a unique key on the word column. This constraint ensures a duplicate word cannot be added.

Is every NULL unique in SQL?

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.

Can we use unique and not null together?

Yes, it's possible.

Can unique key column have NULL values?

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

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