TCL

Affairs

Sql statement or a group consisting of one execution unit, the execution unit performs either all, or all not be executed.

1. Transaction characteristics:

   ACID
   Atomicity: a transaction can not be subdivided, either perform or not perform
   Consistency: a transaction data will perform handover from one consistent state to another consistent state
   Isolation: performing a transaction without interference from other transactions
   lasting sex: once a transaction is committed, the data will be permanent changes to the database.

2. Creating a transaction

• Implicit transaction: Transaction no apparent opening and closing tags
  such as insert, update, delete statement

• Explicit transaction: The transaction has a significant opening and mark the end of
  the premise: You must set up automatic submission function is disabled, set autocommit = 0;

#步骤1：开启事务
set autocommit=0;
start transaction;可选的

#步骤2：编写事务中的sql语句(select insert update delete)
语句1;
语句2;
...

#步骤3：结束事务
commit;提交事务
rollback;回滚事务

savepoint 节点名;设置保存点

# savepoint 的使用
SET autocommit=0;
START TRANSACTION;
DELETE FROM account WHERE id=25;
SAVEPOINT a;#设置保存点
DELETE FROM account WHERE id=28;
ROLLBACK TO a;#回滚到保存点

1. Transaction isolation level:

	Dirty read	Non-repeatable read	Magic Reading
read uncommitted	√	√	√
read committed	×	√	√
repeatable read	×	×	√
serializable	×	×	×

The third default mysql isolation level Read Repeatable
Oracle default second read committed isolation level

• To view the isolation level
  select @@ tx_isolation;
• Setting the isolation level
  set session | global transaction isolation level isolation level;