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【赛迪网－it技术报道】问题：where timestamp>date 这种子句是走索引吗?
下面我们针对这个问题做一个试验：
c:>sqlplus / as sysdba
sys@eos >create table test as select table_name,to_timestamp(last_analyzed) date_test from dba_tables;
表已创建。
sys@eos> create index idx_test_date on test (date_test);
索引已创建。
sys@eos> desc test
名称 是否为空? 类型
------------------------- -------- ----------------
table_name not null varchar2(30)
date_test timestamp(0)
sys@eos> select date_test from test where date_test > to_date('2007-11-5 00:00:00','yyyy-mm-dd hh24:mi:ss');
执行计划
----------------------------------------------------------
plan hash value: 944171586
-------------------------------------------------------------------------------- --
| id | operation | name | rows | bytes | cost (%cpu)| time |
-------------------------------------------------------------------------------- --
| 0 | select statement | | 1 | 22 | 1 (0)| 00:00:01 |
|* 1 | index range scan| idx_test_date | 1 | 22 | 1 (0)| 00:00:01 |
-------------------------------------------------------------------------------- --
predicate information (identified by operation id):
---------------------------------------------------
1 - access("date_test">timestamp'2007-11-05 00:00:00')
note
-----
- dynamic sampling used for this statement
统计信息
----------------------------------------------------------
7 recursive calls
0 db block gets
18 consistent gets
0 physical reads
0 redo size
280 bytes sent via sql*net to client
374 bytes received via sql*net from client
1 sql*net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
从上文中大家可以清楚地看到，timestamp>date情况下，走索引。
另外，date类型一般很少用，建议大家在产品里面所有的date数据类型全部改为timestamp。
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