What could be the reason?

View Exhibit1 and examine the indexes on the CUSTOMERS table.

The statistics for the CUSTOMERS table have been updated recently by using the following command:
SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS(‘SH’,’CUSTOMERS’,method_opt=>’FOR
ALL
INDEXED COLUMNS SIZE AUTO’);
View Exhibit2 to examine a query plan. Even though the index is present on the COUNTRY_ID
and CUST_GENDER columns, the query uses a full table scan. What could be the reason?

View Exhibit1 and examine the indexes on the CUSTOMERS table.

The statistics for the CUSTOMERS table have been updated recently by using the following command:
SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS(‘SH’,’CUSTOMERS’,method_opt=>’FOR
ALL
INDEXED COLUMNS SIZE AUTO’);
View Exhibit2 to examine a query plan. Even though the index is present on the COUNTRY_ID
and CUST_GENDER columns, the query uses a full table scan. What could be the reason?

A.
because the histogram statistics for the COUNTRY_ID column are not updated

B.
because the DB_FILE_MULTIBLOCK_READ_COUNT initialization parameter is set to a high
value

C.
because the optimizer calculates the cost of accessing blocks by using a full table scan to be
less as compared to index scans, even though indexes are available

D.
because indexes on CUST_GENDER and COUNTRY_ID columns are of different types, the
index on the CUST_GENDER column is bitmap index, and on COUNTRY_ID columns is btree
index.



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L. Zhu

L. Zhu

for cost based optimizer, it chooses less cost plan.

So C is correct