blockscout/priv/repo/migrations/20180117221922_create_transactions.exs

defmodule Explorer.Repo.Migrations.CreateTransactions do
  use Ecto.Migration

  def change do
    create table(:transactions) do
      add :hash, :string, null: false
      add :block_id, references(:blocks), null: false
      timestamps null: false
    end

    create unique_index(:transactions, ["(lower(hash))"], name: :transactions_hash_index)
    create index(:transactions, [:block_id])
  end
end