请教一个sql效率的问题，关于常量表达式的

Question

select 常量表达式,　其它字段 from 表名;
例如
select to_char(sysdate, 'yyyy'), cloumn1 from tables;这样的sql，我一直以为数据库会在分析sql时做一些优化
将to_char(sysdate, 'yyyy')
转换成常量2010　sql执行效率应该与
select '2010',  cloumn1 from tables;
相当但今天听人家没这回事，不知道是不是这样？如果是的话有没有什么办法让数据库做出这样的优化呢？

Answer 1

执行计划能看出什么吗 我看不出来 下面是两者的执行计划
select * from table(dbms_xplan.display);
select * from table(dbms_xplan.display);PLAN_TABLE_OUTP                                     
------------------------------------------------------
                                                      
------------------------------------------------------
| Id  | Operation        | Name | Rows  | Cost (%CPU)|
------------------------------------------------------
|   0 | SELECT STATEMENT |      |     1 |     2   (0)|
|   1 |  FAST DUAL       |      |     1 |     2   (0)|
------------------------------------------------------
                                                      
Note                                                  
-----                                                 
   - 'PLAN_TABLE' is old version                      
explain plan for select 2010 from dual;
select * from table(dbms_xplan.display);PLAN_TABLE_OUTP                                     
------------------------------------------------------
                                                      
------------------------------------------------------
| Id  | Operation        | Name | Rows  | Cost (%CPU)|
------------------------------------------------------
|   0 | SELECT STATEMENT |      |     1 |     2   (0)|
|   1 |  FAST DUAL       |      |     1 |     2   (0)|
------------------------------------------------------
                                                      
Note                                                  
   - 'PLAN_TABLE' is old version