标量子查询优化外连接

标签：优化   数据库   执行计划   oracle   

同事发来2个语句，说语句1跑得慢，语句2很快就出结果。一执行，果然很慢。仔细发现，2个语句不等价。

select l.*,o.object_name 
from v$locked_object l left join all_objects o on l.object_id=o.object_id;

select l.*,o.object_name 
from v$locked_object l,all_objects o where l.object_id=o.object_id;

select l.*,o.object_name 
from v$locked_object l,all_objects o where l.object_id=o.object_id(+);

select l.*,(select o.object_name from all_objects o where l.object_id=o.object_id) from v$locked_object l;

标量子查询优化外连接

标签：优化   数据库   执行计划   oracle   

原文地址：http://blog.csdn.net/gdmzlhj1/article/details/39548589