学步园

select count(0) from info_terminal_user a
where trunc(a.REG_DATE,'dd') = sysdate;

执行计划
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=3322 Card=1 Bytes=7)
   1    0   SORT (AGGREGATE)
   2    1     TABLE ACCESS (FULL) OF 'INFO_TERMINAL_USER' (Cost=3322 C
          ard=33176 Bytes=232232)

 select count(0) from info_terminal_user a
where a.REG_DATE > trunc(sysdate,'dd') and a.reg_date<trunc(sysdate+1,'dd')

执行计划
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=3322 Card=1 Bytes=7)
   1    0   SORT (AGGREGATE)
   2    1     FILTER
   3    2       TABLE ACCESS (FULL) OF 'INFO_TERMINAL_USER' (Cost=3322
           Card=1160 Bytes=8120)


2.总结:日期条件出现的时候尽量不要在日期字段上面做运算,把运算转移到字段的外边;