diff --git a/brmbar3/SQL b/brmbar3/SQL
index a61dba8..04667f4 100644
--- a/brmbar3/SQL
+++ b/brmbar3/SQL
@@ -1,11 +1,11 @@
-CREATE SEQUENCE currencies_id_seq START WITH 1 INCREMENT BY 1;
+CREATE SEQUENCE currencies_id_seq START WITH 2 INCREMENT BY 1;
 CREATE TABLE currencies (
 	id INTEGER PRIMARY KEY NOT NULL DEFAULT NEXTVAL('currencies_id_seq'::regclass),
 	name VARCHAR(128) NOT NULL,
 	UNIQUE(name)
 );
 -- Some code depends on the primary physical currency to have id 1.
-INSERT INTO currencies (name) VALUES ('Kč');
+INSERT INTO currencies (id, name) VALUES (1, 'Kč');
 
 CREATE TYPE exchange_rate_direction AS ENUM ('source_to_target', 'target_to_source');
 CREATE TABLE exchange_rates (
diff --git a/brmbar3/SQL-schema-v002.sql b/brmbar3/SQL-schema-v002.sql
new file mode 100644
index 0000000..afe6c80
--- /dev/null
+++ b/brmbar3/SQL-schema-v002.sql
@@ -0,0 +1,80 @@
+-- intoduce implementation schema
+CREATE SCHEMA IF NOT EXISTS brmbar_implementation;
+-- version table (with initialization)
+CREATE TABLE IF NOT EXISTS brmbar_implementation.brmbar_schema (
+	ver INTEGER NOT NULL
+);
+DO $$
+DECLARE v INTEGER;
+BEGIN
+	SELECT ver FROM brmbar_implementation.brmbar_schema INTO v;
+	IF v IS NULL THEN
+		INSERT INTO brmbar_implementation.brmbar_schema (ver) VALUES (1);
+	END IF;
+END;
+$$;
+
+
+--- upgrade schema
+DO $$
+DECLARE
+current_ver INTEGER;
+BEGIN
+
+SELECT ver FROM brmbar_implementation.brmbar_schema INTO current_ver;
+IF current_ver <> 1 THEN
+	RAISE EXCEPTION 'BrmBar schema version % cannot be upgraded to version 2.', current_ver;
+END IF;
+
+ALTER TYPE public.account_type ADD VALUE 'trading';
+
+--drop function if exists public.create_currency;
+CREATE OR REPLACE PROCEDURE public.create_currency(
+	IN i_name public.currencies.name%TYPE,
+	OUT o_id public.currencies.id%TYPE)
+LANGUAGE plpgsql SECURITY DEFINER AS $fn$
+BEGIN
+        INSERT INTO currencies ("name") VALUES (i_name) RETURNING o_id;
+END
+$fn$;
+
+CREATE OR REPLACE PROCEDURE public.undo_transaction(
+	IN i_id public.transactions.id%TYPE,
+	OUT o_id public.transactions.id%TYPE)
+LANGUAGE plpgsql SECURITY DEFINER AS $fn$
+DECLARE
+	v_ntrn_id public.transactions.id%TYPE;
+	v_old_trn public.transactions%ROWTYPE;
+	v_old_split public.transaction_splits%ROWTYPE;
+BEGIN
+	SELECT * INTO v_old_trn FROM public.transactions WHERE id = i_id;
+        INSERT INTO transactions ("description") VALUES ('undo '||o_id||' ('||v_old_trn.description||')') RETURNING id into v_ntrn_id;
+	FOR v_old_split IN
+		SELECT * FROM transaction_splits WHERE "transaction" = i_id
+	LOOP
+		INSERT INTO transaction_splits ("transaction", "side", "account", "amount", "memo")
+		VALUES (v_ntrn_id, v_old_split.side, v_old_split.account, -v_old_split.amount,
+			'undo ' || v_old_split.id || ' (' || v_old_split.memo || ')' );
+	END LOOP;
+	o_id := v_ntrn_id;
+END
+$fn$;
+
+-- this is for the case that psycopg2 cannot do output arguments
+CREATE OR REPLACE FUNCTION public.undo_transaction_fn(
+	IN i_id public.transactions.id%TYPE)
+RETURNS public.transactions.id%TYPE
+VOLATILE  NOT LEAKPROOF  LANGUAGE plpgsql AS $fn$
+DECLARE
+	v_ntrn_id public.transactions.id%TYPE;
+BEGIN
+	CALL public.undo_transaction(i_id, v_ntrn_id);
+	RETURN v_ntrn_id;
+END
+$fn$;
+
+
+-- end of upgrade do block
+end
+$$;
+
diff --git a/brmbar3/brmbar/Shop.py b/brmbar3/brmbar/Shop.py
index 6027084..5049fcc 100644
--- a/brmbar3/brmbar/Shop.py
+++ b/brmbar3/brmbar/Shop.py
@@ -219,14 +219,15 @@ class Shop:
         self.db.commit()
 
     def undo(self, oldtid):
-        description = self.db.execute_and_fetch("SELECT description FROM transactions WHERE id = %s", [oldtid])[0]
-        description = 'undo %d (%s)' % (oldtid, description)
+        #description = self.db.execute_and_fetch("SELECT description FROM transactions WHERE id = %s", [oldtid])[0]
+        #description = 'undo %d (%s)' % (oldtid, description)
 
-        transaction = self._transaction(description=description)
-        for split in self.db.execute_and_fetchall("SELECT id, side, account, amount, memo FROM transaction_splits WHERE transaction = %s", [oldtid]):
-            splitid, side, account, amount, memo = split
-            memo = 'undo %d (%s)' % (splitid, memo)
-            amount = -amount
-            self.db.execute("INSERT INTO transaction_splits (transaction, side, account, amount, memo) VALUES (%s, %s, %s, %s, %s)", [transaction, side, account, amount, memo])
+        #transaction = self._transaction(description=description)
+        #for split in self.db.execute_and_fetchall("SELECT id, side, account, amount, memo FROM transaction_splits WHERE transaction = %s", [oldtid]):
+        #    splitid, side, account, amount, memo = split
+        #    memo = 'undo %d (%s)' % (splitid, memo)
+        #    amount = -amount
+        #    self.db.execute("INSERT INTO transaction_splits (transaction, side, account, amount, memo) VALUES (%s, %s, %s, %s, %s)", [transaction, side, account, amount, memo])
+        transaction = self.db.execute_and_fetch("CALL undo_transaction(%s)",[oldtid])[0]
         self.db.commit()
         return transaction