Add database schema and migration tasks

db/migrations/002_create_members.rb

@@ -0,0 +1,35 @@
+Sequel.migration do
+  up do
+    create_table(:members) do
+      primary_key :id, type: :Bignum
+
+      foreign_key :account_id, :accounts,
+        type: :Bignum,
+        null: false
+
+      String :kind, null: false
+      String :first_name
+      String :last_name
+      String :organization_name
+
+      index :account_id, unique: true
+
+      constraint :members_kind_valid,
+        Sequel.lit("kind IN ('individual', 'organization')")
+
+      constraint :members_identity_matches_kind,
+        Sequel.lit(
+          "(kind = 'individual' AND first_name IS NOT NULL " \
+          "AND trim(first_name) <> '' AND last_name IS NOT NULL " \
+          "AND trim(last_name) <> '' AND organization_name IS NULL) " \
+          "OR (kind = 'organization' AND first_name IS NULL " \
+          "AND last_name IS NULL AND organization_name IS NOT NULL " \
+          "AND trim(organization_name) <> '')"
+        )
+    end
+  end
+
+  down do
+    drop_table(:members)
+  end
+end