rollback的功能在数据库中都一样，未提交的操作都会回滚，在psql中默认配置下AUTOCOMMIT是打开的，这一点和oracle不同，
如果测试需要先把autocommit设置为off，
\set AUTOCOMMIT off
在postgresql中有个savepoint可以回滚到某个点

1. 做几个测试，创建多个savepoint点，并可以多次rollback到同一个savepoint，rollback至savepoint后可以继续操作
postgres=# \set AUTOCOMMIT off
insert into tt values(1);
insert into tt values(2);
savepoint savepoint1;
insert into tt values(3);
insert into tt values(4);
savepoint savepoint2;
insert into tt values(5);
insert into tt values(6);postgres=# INSERT 0 1
postgres=# INSERT 0 1
postgres=# SAVEPOINT
postgres=# INSERT 0 1
postgres=# INSERT 0 1
postgres=# SAVEPOINT
postgres=# INSERT 0 1
postgres=# 
INSERT 0 1
postgres=# 
postgres=# select * from tt;
 t1 
----
 1
 2
 3
 4
 5
 6
(6 rows)
 
postgres=# rollback to savepoint savepoint2;
ROLLBACK
postgres=# select * from tt;
 t1 
----
 1
 2
 3
 4
(4 rows)
 
postgres=# insert into tt values(5);
INSERT 0 1
postgres=# select * from tt;
 t1 
----
 1
 2
 3
 4
 5
(5 rows)
 
postgres=# rollback to savepoint savepoint2;
ROLLBACK
postgres=# select * from tt;
 t1 
----
 1
 2
 3
 4
(4 rows)
 
postgres=# commit;
COMMIT
postgres=# 
postgres=# select * from tt;
 t1 
----
 1
 2
 3
 4
(4 rows)

2.在rollback至savepoint后操作如果出错，后续的所有操作会报
ERROR:  current transaction is aborted, commands ignored until end of transaction block
这时候需要再次rollback to savepoint2可以回滚至savepoint2。
\set AUTOCOMMIT off
insert into tt values(1);
insert into tt values(2);
savepoint savepoint1;
insert into tt values(3);
insert into tt values(4);
savepoint savepoint2;
insert into tt values(5);
insert into tt values(6);

回滚
postgres=# rollback to savepoint savepoint2;
ROLLBACK
postgres=# select * from tt;
 t1 
----
 1
 2
 3
 4
(4 rows)
 
postgres=# insert into tt values('dfsdfdsf','sdf');
ERROR:  INSERT has more expressions than target columns
LINE 1: insert into tt values('dfsdfdsf','sdf');
                                         ^
postgres=# select * from tt;
ERROR:  current transaction is aborted, commands ignored until end of transaction block
postgres=# \d tt
ERROR:  current transaction is aborted, commands ignored until end of transaction block
postgres=# ;
postgres=# select * from tt;
ERROR:  current transaction is aborted, commands ignored until end of transaction block
postgres=# rollback to savepoint savepoint2;
ROLLBACK
postgres=# select * from tt;
 t1 
----
 1
 2
 3
 4
(4 rows)