Used internally by adapters.
To define a constraint in a migration, see Ecto.Migration.constraint/3.
Ecto.Migration.constraint/3
@type t() :: %Ecto.Migration.Constraint{ check: String.t() | nil, comment: String.t() | nil, exclude: String.t() | nil, name: atom(), prefix: String.t() | nil, table: String.t(), validate: boolean() }