SQL>select * from v$version;
BANNER
----------------------------------------------------------------
Oracle9i Enterprise Edition Release 9.2.0.4.0 - 64bit Production
PL/SQL Release 9.2.0.4.0 - Production
CORE 9.2.0.3.0 Production
TNS for Solaris: Version 9.2.0.4.0 - Production
NLSRTL Version 9.2.0.4.0 - Production
SQL>create table t_test3 as select * from dba_tables;
Table created.
SQL>analyze table t_test3 compute statistics;
Table analyzed.
SQL>select avg_row_len,num_rows,blocks from user_tables where table_name = 'T_TEST3';
AVG_ROW_LEN NUM_ROWS BLOCKS
----------- ---------- ----------
188 5502 146
SQL>analyze table t_test3 delete statistics;
Table analyzed.
SQL>exec dbms_stats.gather_table_stats(user,'T_TEST3');
PL/SQL procedure successfully completed.
SQL>select avg_row_len,num_rows,blocks from user_tables where table_name = 'T_TEST3';
AVG_ROW_LEN NUM_ROWS BLOCKS
----------- ---------- ----------
183 5502 146
SQL>
默认dbms_stats.gather_table_stats分析表得到平均行长貌视少一些。
SQL>create table t_test4 as select * from t_test3;
Table created.
SQL>exec dbms_stats.gather_table_stats(user,'T_TEST4',estimate_percent=>100);
PL/SQL procedure successfully completed.
SQL>select avg_row_len,num_rows,blocks from user_tables where table_name = 'T_TEST4';
AVG_ROW_LEN NUM_ROWS BLOCKS
----------- ---------- ----------
183 5502 146
SQL>
dbms_stats.gather_table_stats的输入参数estimate_percent为100（即100%评估），分析表得到平均行长就是准确了
