用最简单的方法记录Oracle语句的执行时间

[oracle@jw ~]$ sqlplus "/as sysdba"
SQL*Plus: Release 9.2.0.4.0 - Production on 
星期二 8月 28 16:59:43 2007
Copyright (c) 1982, 2002, Oracle 
Corporation. All rights reserved.

Oracle9i Enterprise Edition 
Release 9.2.0.4.0 - Production
With the Partitioning, Oracle Label Security, 
OLAP and Oracle Data Mining options
JServer Release 9.2.0.4.0 - Production
SQL> set timing on;
SQL> select count(*) from tab;

COUNT(*)
----------
2447

已用时间: 00: 00: 00.12
SQL>