This option is available in Postgres 11 and later. I recently needed to enforce a database constraint similar in spirit to a unique index, however the criteria for what should be considered “unique” was more complex than what a simple unique index in PostgreSQL would be able to deal with. They state that column or a number of group of column rows values are unique in all rows in the tables. PostgreSQL unique constraint is straight that all the records in table column are unique, duplicates are not allowed in PostgreSQL unique constraint. PostgreSQL Unique Constraint. The preferred way to add a unique constraint to a table is ALTER TABLE ... ADD CONSTRAINT. Postgres implements unique constraints by creating a unique index – an index that can only contain unique values. This option is available in Postgres 11 and later. Adding UNIQUE constraints to tables in Postgres is very easy! The other forms are PostgreSQL extensions of the SQL standard. The UNIQUE constraint in PostgreSQL violated when more than one row for a column or combination of columns which have been used as a unique constraint in a table. Two NULL values for a column in different rows is different and it does not violate the uniqueness of UNIQUE constraint. Imagine we have the following table: CREATE TABLE users ( id uuid PRIMARY KEY NOT NULL DEFAULT uuid_generate_v4(), email text ); If we want to ensure that each user has a unique email we simply add: ALTER TABLE users ADD CONSTRAINT email_unique UNIQUE (email); create unique index unique_row on myTable(content_id, brand_id) where not is_archived; See Partial Indexes in the Postgres documentation. Adding a unique constraint will automatically create a unique B-tree index on the column or column group listed in the constraint. Complex Unique Constraints with PostgreSQL Triggers in Ecto. In this section, we are going to understand the working of the PostgreSQL UNIQUE constraint, which is used to make sure that all values in a column of a table are exclusive.. Use Include columns field to specify columns for INCLUDE clause of the constraint. Also, the ability to specify more than one manipulation in a single ALTER TABLE … Select the name of an index from the drop-down listbox in the Index field. The unique constraint should be different from the primary key constraint defined for the same table; the selected column(s) for the constraints must be distinct. How Postgres Unique Constraints Can Cause Deadlock. 3. Modify the table. PostgreSQL 11.2 add constraints, delete constraints, add columns, delete columns. This is effectively pretty much the same as a unique constraint, because such constraints are implemented with unique indexes anyway. The use of indexes to enforce unique constraints could be considered an implementation detail that should not be accessed directly. 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