ORACLE的表分析策略

对表进行分析，通常情况下可以对表，索引，列进行单独分析，或者进行组合分析，但这三者哪些是相对重要的，哪些分析显得不那么重要？通过本篇文章的实验相信大家也会对直方图有更一步的了解.
1.首先创建测试表,并插入100000条数据
SQL> create table test(id number,nick varchar2(30));
Table created.
SQL> begin
  2      for i in 1..100000 loop
  3            insert into test(id) values(i);
  4      end loop;
  5      commit;
  6  end;
  7  /
PL/SQL procedure successfully completed.
更新nick字段，使数据发生严重倾斜
SQL> update test set nick='abc' where rownum<99999; 
99998 rows updated.
SQL> commit;
Commit complete.
SQL> create index idx_test_nick on test(nick);
Index created.
SQL> update test set nick='def' where nick is null;
2 rows updated.
SQL> commit;
Commit complete.
--只对索引进行分析
SQL> analyze index idx_test_nick compute statistics;
Index analyzed.
SQL> select index_name,LEAF_BLOCKS,DISTINCT_KEYS,NUM_ROWS from user_indexes where index_name='IDX_TEST_NICK';
INDEX_NAME                     LEAF_BLOCKS DISTINCT_KEYS   NUM_ROWS
------------------------------ ----------- ------------- ----------
IDX_TEST_NICK                          210             2     100000
SQL> select COLUMN_NAME,NUM_BUCKETS,num_distinct from USER_tab_columns where table_name='TEST';
COLUMN_NAME                    NUM_BUCKETS NUM_DISTINCT
------------------------------