Additionally, users can maintain different sets of statistics within a single stattab by using the statid parameter, which can help avoid cluttering the user's schema.

灵位，我们也可以指定statid参数，从而在相同的stattab中存储不同的统计信息，这样可以使用户模式显得井井有条。

For all of the SET or GET procedures, if stattab is not provided (i.e., NULL), then the operation works directly on the dictionary statistics; therefore, users do not need to create these statistics tables if they only plan to modify the dictionary directly. However, if stattab is not NULL, then the SET or GET operation works on the specified user statistics table, and not the dictionary.

对于所有的set和get过程，如果我们没有指定stattab，oracle会将统计信息写入数据字典，如果指定了stattab，orcle只会将统计信息写入用户自定义表，而不会更新数据字典。

Create Stats Table

DBMS_STATS.CREATE_STAT_TABLE (
  ownname  VARCHAR2, 
  stattab  VARCHAR2,
  tblspace VARCHAR2 DEFAULT NULL);

stattab : Name of the table to create. This value should be passed as the stattab parameter to other procedures when the user does not want to modify the dictionary statistics directly. tblspace : Tablespace in which to create the stat tables. If none is specified, then they are created in the user's default tablespace.

Drop Stats Table

DBMS_STATS.drop_stat_table (
  ownname VARCHAR2, 
  stattab VARCHAR2);

stattab : User stat table identifier.

Gather Schema Stats (本人在测试过程中，即便指定了stattab，该过程依然更新了数据字典)

DBMS_STATS.gather_schema_stats (
  ownname          VARCHAR2,
  estimate_percent NUMBER   DEFAULT NULL, 
  block_sample     BOOLEAN  DEFAULT FALSE,
  method_opt       VARCHAR2 DEFAULT 'FOR ALL COLUMNS SIZE 1',（size 1 指在该列上不创建histogram，如果该值大于1，则创建histogram）
  degree           NUMBER   DEFAULT NULL,
  granularity      VARCHAR2 DEFAULT 'DEFAULT', 
  cascade          BOOLEAN  DEFAULT FALSE,
  stattab          VARCHAR2 DEFAULT NULL, 
  statid           VARCHAR2 DEFAULT NULL,
  options          VARCHAR2 DEFAULT 'GATHER', 
  objlist     OUT  ObjectTab,
  statown          VARCHAR2 DEFAULT NULL);

estimate_percent : Percentage of rows to estimate (NULL means compute): The valid range is [0.000001,100).

block_sample : Whether or not to use random block sampling instead of random row sampling. Random block sampling is more efficient, but if the data is not randomly distributed on disk, then the sample values may be somewhat correlated. Only pertinent when doing an estimate statistics.

method_opt : Method options of the following format (the phrase 'SIZE 1' is required to ensure gathering statistics in parallel and for use with the phrase hidden):

FOR ALL [INDEXED | HIDDEN] COLUMNS [SIZE integer]

This value is passed to all of the individual tables.

degree : Degree of parallelism (NULL means use table default value).

granularity : Granularity of statistics to collect (only pertinent if the table is partitioned).