begin tran a
select @@trancount
save tran a /*保持外层事务*/
begin tran b
select @@trancount
rollback tran a /*回滚内层事务*/
commit tran a
select @@trancount
save tran a /*保持外层事务*/
begin tran b
select @@trancount
rollback tran a /*回滚内层事务*/
commit tran a
select @@trancount
save tran tran_a /*保存外层事务,名称为tran_a*/
begin tran b
select @@trancount
rollback tran tran_a /*回滚到已保存的外层事务tran_a处*/
commit tran a