多选题Which two statements are true regarding the execution of the correlated subqueries？（）AThe nested query executes after the outer query returns the row.BThe nested query executes first and then the outer query executes.CThe outer query executes only once

第1题：

Which three statements are true regarding subqueries?（）

• A、Subqueries can contain GROUP BY and ORDER BY clauses 
• B、Main query and subquery can get data from different tables 
• C、Main query and subquery must get data from the same tables 
• D、Subqueries can contain ORDER BY but not the GROUP BY clause 
• E、Only one column or expression can be compared between the main query and subquery
• F、 Multiple columns or expressions can be compared between the main query and subquery

第2题：

Which two statements about subqueries are true? （）

• A、A subquery should retrieve only one row.
• B、A subquery can retrieve zero or more rows.
• C、A subquery can be used only in SQL query statements.
• D、Subqueries CANNOT be nested by more than two levels.
• E、A subquery CANNOT be used in an SQL query statement that uses group functions.
• F、When a subquery is used with an inequality comparison operator in the outer SQL statement, the column list in the SELECT clause of the subquery should contain only one column.

第3题：

What is true regarding subqueries?（）

• A、The inner query always sorts the results of the outer query
• B、The outer query always sorts the results of the inner query
• C、The outer query must return a value to the outer query
• D、The inner query returns a value to the outer query
• E、The inner query must always return a value or the outer query will give an error

第4题：

You define a multiple-row subquery in the WHERE clause of an SQL query with a comparison operator "=". What happens when the main query is executed? （）

• A、The main query executes with the first value returned by the subquery.
• B、The main query executes with the last value returned by the subquery.
• C、The main query executes with all the values returned by the subquery.
• D、The main query fails because the multiple-row subquery cannot be used with the comparison operator.
• E、You cannot define a multiple-row subquery in the WHERE clause of a SQL query.

第5题：

Examine the parameters for your database instance: Which three statements are true about the process of automatic optimization by using cardinality feedback?（）

• A、The optimizer automatically changes a plan during subsequent execution of a SQL statement if there is a huge difference in optimizer estimates and execution statistics.
• B、The optimizer can re optimize a query only once using cardinality feedback.
• C、The optimizer enables monitoring for cardinality feedback after the first execution of a query.
• D、The optimizer does not monitor cardinality feedback if dynamic sampling and multicolumn statistics are enabled.
• E、After the optimizer identifies a query as a re-optimization candidate, statistics collected by the collectors are submitted to the optimizer.

第6题：

Top N analysis requires （） and （）.

• A、the use of rowid
• B、a GROUP BY clause
• C、an ORDER BY clause
• D、only an inline view
• E、an inline view and an outer query

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第13题：

Examine the parameter for your database instance: You generated the execution plan for the following query in the plan table and noticed that the nested loop join was done. After actual execution of the query, you notice that the hash join was done in the execution plan: Identify the reason why the optimizer chose different execution plans.（）

• A、The optimizer used a dynamic plan for the query.
• B、The optimizer chose different plans because automatic dynamic sampling was enabled.
• C、The optimizer used re-optimization cardinality feedback for the query.
• D、The optimizer chose different plan because extended statistics were created for the columns used.

第14题：

Which three statements about subqueries are true? （）

• A、A main query can have more than one subquery.
• B、A subquery can have more than one main query.
• C、The subquery and main query must retrieve data from the same table.
• D、The subquery and main query can retrieve data from different tables.
• E、Only one column or expression can be compared between the subquery and main query.
• F、Multiple columns or expression can be compared between the subquery and main query.

第15题：

You are using the Database Resource Manager to manage database resources. You created a resource plan directive for the MANAGERS resource consumer group under the SALES_PLAN by using the following statement：   SQL>EXEC DBMS_RESOURCE_MANAGER.CREATE_PLAN_DIRECTIVE   （PLAN => ’SALES_PLAN’，   GROUP_OR_SUBPLAN => ’MANAGERS’，   CPU_P1 => 100， CPU_P2 =>0，   SWITCH_GROUP => ’CLERKS’，   SWITCH_TIME_IN_CALL => 600）；   A user， SCOTT， who is assigned to the MANAGERS group， starts a database session and executes a query on the database. What is the outcome if the query takes approximately 15 minutes to complete？（）  

• A、 The query starts under the CLERKS group and the user， SCOTT， switches back to the MANAGERS group after the query completes.
• B、 The query starts under the MANAGERS group but terminates with an error when the execution time exceeds 10 minutes.
• C、 The query starts under the MANAGERS group and switches automatically to the CLERKS group when the execution time exceeds 10 minutes. The query does not switch back to the MANAGERS group after the query completes.
• D、 The query starts under the MANAGERS group， the user SCOTT switches automatically to the CLERKS group when the execution time exceeds 10 minutes， and then switches back to the MANAGERS group after the query completes.

第16题：

Which two statements are true regarding subqueries? （）

• A、A subquery can retrieve zero or more rows 
• B、Only two subqueries can be placed atone level 
• C、A subquery can be used only in SQL query statements 
• D、A subquery can appear on either side of a comparison operator 
• E、There is no limit on the number of subquery levels in the WHERE clause of a SELECT statement 

第17题：

What is true regarding subqueries?（）

• A、The inner query always sorts the results of the outer query.
• B、The outer query always sorts the results of the inner query.
• C、The outer query must return a value to the inner query.
• D、The inner query returns a value to the outer query.
• E、The inner query must always return a value or the outer query will give an error.

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