You want to capture column group usage and gather extended statistics for better cardinality estimates for the
CUSTOMERS table in the SH schema.
Examine the following steps:
1. Issue the SELECT DBMS_STATS.CREATE_EXTENDED_STATS (‘SH’, ‘CUSTOMERS’) FROM dual
statement.
2. Execute the DBMS_STATS.SEED_COL_USAGE (null, ‘SH’, 500) procedure.
3. Execute the required queries on the CUSTOMERS table.
4. Issue the SELECT DBMS_STATS.REPORT_COL_USAGE (‘SH’, ‘CUSTOMERS’) FROM dual statement.
Identify the correct sequence of steps.
A.
3, 2, 1, 4
B.
2, 3, 4, 1
C.
4, 1, 3, 2
D.
3, 2, 4, 1
Explanation:
Step 1 (2). Seed column usage
Oracle must observe a representative workload, in order to determine the appropriate column groups. Using
the new procedure DBMS_STATS.SEED_COL_USAGE, you tell Oracle how long it should observe the
workload.
Step 2: (3) You don’t need to execute all of the queries in your work during this window. You can simply run
explain plan for some of your longer running queries to ensure column group information is recorded for these
queries.
Step 3. (1) Create the column groups
At this point you can get Oracle to automatically create the column groups for each of the tables based on the
usage information captured during the monitoring window. You simply have to call the
DBMS_STATS.CREATE_EXTENDED_STATS function for each table.This function requires just two
arguments, the schema name and the table name. From then on, statistics will be maintained for each column
group whenever statistics are gathered on the table.
Note:
* DBMS_STATS.REPORT_COL_USAGE reports column usage information and records all the SQL operations
the database has processed for a given object.* The Oracle SQL optimizer has always been ignorant of the implied relationships between data columns within
the same table. While the optimizer has traditionally analyzed the distribution of values within a column, he
does not collect value-based relationships between columns.
* Creating extended statisticsHere are the steps to create extended statistics for related table columns
withdbms_stats.created_extended_stats:
1 – The first step is to create column histograms for the related columns.2 – Next, we run
dbms_stats.create_extended_stats to relate the columns together.
Unlike a traditional procedure that is invoked via an execute (“exec”) statement, Oracle extended statistics are
created via a select statement.