Does unique index allow NULL Postgres?

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Introduction to PostgreSQL UNIQUE index PostgreSQL treats NULL as distinct value, therefore, you can have multiple NULL values in a column with a UNIQUE index. When you define a primary key or a unique constraint for a table, PostgreSQL automatically creates a corresponding UNIQUE index.

Can unique index have NULL values Postgres?

When an index is declared unique, multiple table rows with equal indexed values are not allowed. Null values are not considered equal. A multicolumn unique index will only reject cases where all indexed columns are equal in multiple rows.

Can a unique index be NULL?

Although null values represent unknown values, when it comes to indexing, a null value is treated as being equal to other null values. Therefore, if a unique index consists of a single column, only one null value is allowed-more than one null value would violate the unique constraint.

Can you insert NULL in unique column?

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. This means that it's possible to insert rows that appear to be duplicates if one of the values is NULL .

Can unique key accept NULL?

Primary key will not accept NULL values whereas Unique key can accept NULL values. A table can have only one primary key whereas there can be multiple unique key on a table. A Clustered index automatically created when a primary key is defined whereas Unique key generates the non-clustered index.

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