sql server 事务隔离性 snapshot 、read committed说明

 --该 read committed 默认事务隔离级别 在 systemuser修改事务未完成时   select * from  [SystemUser]  where id=62; 该语句是不可读取的

set transaction  isolation level   read committed;

begin transaction   

update [SystemUser] set LoginId=‘test‘ where id=62;

 waitfor delay ‘00:00:10‘
  
commit transaction; 
go


--可新建查询窗口
begin transaction   readtran

 select * from  [SystemUser]  where id=62; 
commit transaction;


二、 需手动设置  读提交快照处理打开状态 设置为true —— 右键数据——选项——读提交快照处理打开状态
在 allow_snapshot_isolation on    和 set transaction  isolation level   snapshot ;模式下事务未执行完是可以读取数据的
  -- 开启快照隔离
  --alter database [SimpleFactoring15] set allow_snapshot_isolation on 
  -- 关闭快照隔离
 --alter database [SimpleFactoring15] set allow_snapshot_isolation off


  -- 开启快照隔离
 alter database [SimpleFactoring15] set allow_snapshot_isolation on 
 set transaction  isolation level   snapshot ;

begin transaction   

update [SystemUser] set LoginId=‘开启快照隔离‘ where id=62;

 waitfor delay ‘00:00:10‘
  
commit transaction; 
go


--可新建查询窗口
begin transaction   readtran

 select * from  [SystemUser]  where id=62; 
commit transaction;