OCP-1Z0-053-V13.02-490题

490.View the Exhibit.

Examine the following command that is executed for the TRANSPORT table in the SH schema:

SQL> SELECT DBMS_STATS.CREATE_EXTENDED_STATS('sh', 'customers_obe',

'(country_id, cust_state_province)') FROM dual;

Which statement describes the significance of this command?

A. It collects statistics into the pending area in the data dictionary.

B. It creates a virtual hidden column in the CUSTOMERS_OBE table.

C. It collects statistics with AUTO_SAMPLE_SIZE for ESTIMATE_PERCENT.

D. It creates a histogram to hold skewed information about the data in the columns.

Answer: B

答案解析：

参考：http://docs.oracle.com/cd/E11882_01/server.112/e41573/stats.htm#PFGRF94739

CREATE_EXTENDED_STATS Function

Creates a virtual column for a user specified column group or an expression in a table

Creating a Column Group

Use the CREATE_EXTENDED_STATISTICS function to create a column group. The CREATE_EXTENDED_STATISTICS function returns the system-generated name of the newly created column group. Table 13-5 lists the input parameters for this function.

Table 13-5 Parameters for the create_extended_statistics Function

Parameter	Description
ownname	Schema owner. NULL indicates current schema.
tabname	Name of the table to which the column group is added.
extension	Columns in the column group.

For example, to add a column group consisting of the cust_state_province and country_id columns to the customers table in SH schema, run the following PL/SQL block:

DECLARE

  cg_name VARCHAR2(30);

BEGIN

  cg_name := DBMS_STATS.CREATE_EXTENDED_STATS(null,'customers', 

             '(cust_state_province,country_id)');

END;

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