class ActiveRecord::ConnectionAdapters::PostgreSQL::Table

See {connection.add_unique_constraint}[rdoc-ref:SchemaStatements#add_unique_constraint]

t.unique_constraint(:position, name: 'unique_position', deferrable: :deferred, nulls_not_distinct: true)

Adds a unique constraint.

def unique_constraint(...)
  @base.add_unique_constraint(name, ...)
end