-- 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
hll@SZTYORA> 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(SYSDATE@!-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
hll@SZTYORA> 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(SYSDATE@!-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
hll@SZTYORA> 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(SYSDATE@!-1)<TRUNC(SYSDATE@!))
3 - access("CDATE">=TRUNC(SYSDATE@!-1) AND "CDATE"<TRUNC(SYSDATE@!))
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；
