user_tables 的信息依赖于统计信息

all_tables 描述当前用户访问的相关表:

[oracle@node01 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on 星期四 10月 19 09:42:26 2017

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


连接到: 
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> create user tlcb identified by tlcb default tablespace users;

用户已创建。

SQL> grannt dba to tlcb;
SP2-0734: 未知的命令开头 "grannt dba..." - 忽略了剩余的行。
SQL> grant dba to tlcb;

授权成功。


SQL> create table test as select * from dba_objects;

表已创建。


SQL> select count(*) from test;

  COUNT(*)
----------
   1391440

SQL> select a.TABLE_NAME,a.NUM_ROWS,a.LAST_ANALYZED  from user_tables a;

TABLE_NAME			 NUM_ROWS LAST_ANALY
------------------------------ ---------- ----------
TEST


此时没有收集统计信息,没办法从user_tables中获取表的记录数信息


对表进行统计信息收集

BEGIN
  DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'TLCB',
                                tabname          => 'TEST',
                                estimate_percent => 100,
                                method_opt       => 'for all columns size repeat',
                                no_invalidate    => FALSE,
                                degree           => 8,
                                cascade          => TRUE);
END;

SQL>  select a.TABLE_NAME,a.NUM_ROWS,a.LAST_ANALYZED  from user_tables a;

TABLE_NAME			 NUM_ROWS LAST_ANALY
------------------------------ ---------- ----------
TEST				  1391440 2017-10-19

SQL> select count(*) from TEST;

  COUNT(*)
----------
   1391440


user_tables 的准确性,依赖于统计信息。