摘要：
隔离级别(isolation level):定义了事务与事务之间的隔离程度，隔离级别与并发性是互为矛盾的： 隔离程度越高，数据库的并发性越差；隔离程度越低，数据库的并发性越好。 ANSI/ISO SQL92标准定义了一些数据库操作的隔离级别： 1.未提交读（read uncommitted）脏读 2.提交读（read committed）非重复读 3.重复读（repeatable rea... 阅读全文
摘要：
delete from test1 where (id,name )in (select * from ( select id,name from test1 group by id,name having (count(*)>1) ) a) and num not in(select * from ( select min(num) from t... 阅读全文
摘要：
row_number() over(partition by ... order by ...) rank() over(partition by ... order by ...) dense_rank() over(partition by ... order by ...) count() over(partition by ... order by ...) max() over... 阅读全文