Добавил SQL запросы

sql/create-tables.sql

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+CREATE SEQUENCE seq_person;
+CREATE SEQUENCE seq_transaction;
+
+CREATE TABLE person
+(
+    id      BIGINT NOT NULL PRIMARY KEY DEFAULT nextval('seq_person'),
+    balance BIGINT NOT NULL
+);
+
+CREATE TABLE transaction
+(
+    id          BIGINT NOT NULL PRIMARY KEY DEFAULT nextval('seq_transaction'),
+    person_from BIGINT NOT NULL REFERENCES person (id),
+    person_to   BIGINT NOT NULL REFERENCES person (id),
+    amount      BIGINT NOT NULL
+
+);
+
+INSERT INTO person
+VALUES (1, 1000);
+
+INSERT INTO person
+VALUES (2, 1000);

sql/drop-tables.sql

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+drop table transaction cascade;
+
+drop table person cascade;
+
+drop sequence seq_person;
+
+drop sequence seq_transaction;

sql/fail-transaction.sql

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+INSERT INTO person values (1, 100);
+INSERT INTO person values (2, 100);
+
+UPDATE person SET balance = (balance - 10) WHERE id = 1;
+INSERT INTO transaction(person_from, person_to, amount) values (1, 3, 10);
+UPDATE person SET balance = (balance + 10) WHERE id = 2;

sql/refresh-balance.sql

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+DELETE FROM person WHERE id = 3;
+DELETE FROM transaction;
+UPDATE person SET balance = 1000 WHERE id in (1,2)

sql/success-transaction.sql

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+UPDATE person SET balance=100 WHERE id IN (1,2);
+DELETE FROM transaction WHERE person_from = 1;
+
+BEGIN;
+
+UPDATE person SET balance = (balance - 10) WHERE id = 1;
+INSERT INTO transaction(person_from, person_to, amount) values (1, 3, 10);
+UPDATE person SET balance = (balance + 10) WHERE id = 2;
+
+COMMIT;