oracle 查询当天记录 三种方法效率比较

-- 查询一表中当天生成的数据
-- 原表mobilefrends中的cdate字段上有索引，创建索引语句是：create index mobilefrends_cdate_idx on mobilefrends(cdate);

---------------------------------------------------------------------------------------------------------------------
-- 方法一：用to_char()函数

[email protected]> select count(*) from mobilefrends where to_char(cdate,‘yyyy-mm-dd‘)=to_char(sysdate,‘yyyy-mm-dd‘);

  COUNT(*)
----------
     82119

已用时间:  00: 00: 17.18

执行计划
----------------------------------------------------------
Plan hash value: 3731074549

------------------------------------------------------------------------------------------------
| Id  | Operation             | Name                   | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |                        |     1 |     8 | 11773  (16)| 00:02:22 |
|   1 |  SORT AGGREGATE       |                        |     1 |     8 |            |          |
|*  2 |   INDEX FAST FULL SCAN| MOBILEFRENDS_CDATE_IDX |   129K|  1012K| 11773  (16)| 00:02:22 |
------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - filter(TO_CHAR(INTERNAL_FUNCTION("CDATE"),‘yyyy-mm-dd‘)=TO_CHAR([email protected]!-1,‘yyyy
              -mm-dd‘))

统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
      36896  consistent gets
          0  physical reads
          0  redo size
        345  bytes sent via SQL*Net to client
        338  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

---------------------------------------------------------------------------------------------------------------------
-- 方法二：用trunc()函数

[email protected]> select count(*) from mobilefrends where trunc(cdate)=trunc(sysdate);

  COUNT(*)
----------
     82119

已用时间:  00: 00: 16.32

执行计划
----------------------------------------------------------
Plan hash value: 3731074549

------------------------------------------------------------------------------------------------
| Id  | Operation             | Name                   | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |                        |     1 |     8 | 12580  (22)| 00:02:31 |
|   1 |  SORT AGGREGATE       |                        |     1 |     8 |            |          |
|*  2 |   INDEX FAST FULL SCAN| MOBILEFRENDS_CDATE_IDX |   129K|  1012K| 12580  (22)| 00:02:31 |
------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - filter(TRUNC(INTERNAL_FUNCTION("CDATE"))=TRUNC([email protected]!-1))

统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
      36896  consistent gets
          0  physical reads
          0  redo size
        345  bytes sent via SQL*Net to client
        338  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

---------------------------------------------------------------------------------------------------------------------
-- 方法三：不用函数
[email protected]> select count(*) from mobilefrends where cdate>=trunc(sysdate) and cdate<trunc(sysdate)+1;

  COUNT(*)
----------
     82119

已用时间:  00: 00: 00.43

执行计划
----------------------------------------------------------
Plan hash value: 2668176725

---------------------------------------------------------------------------------------------
| Id  | Operation          | Name                   | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |                        |     1 |     8 |     3   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE    |                        |     1 |     8 |            |          |
|*  2 |   FILTER           |                        |       |       |            |          |
|*  3 |    INDEX RANGE SCAN| MOBILEFRENDS_CDATE_IDX |    48 |   384 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - filter(TRUNC([email protected]!-1)<TRUNC([email protected]!))
   3 - access("CDATE">=TRUNC([email protected]!-1) AND "CDATE"<TRUNC([email protected]!))

统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
        221  consistent gets
          0  physical reads
          0  redo size
        345  bytes sent via SQL*Net to client
        338  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

---------------------------------------------------------------------------------------------------------------------

-- 由上三种方法可见：
-- 方法一：用to_char()函数，耗时17.18秒，逻辑读为36896次，执行的是全索引扫描；
-- 方法二：用trunc()函数，耗时16.32秒，逻辑读也是36896次，执行的也是全索引扫描；
-- 方法三：不用函数，耗时0.43秒，逻辑读为221次，执行的是索引范围扫描；

oracle 查询当天记录 三种方法效率比较