多选题Which two statements are true regarding subqueries? （）AA subquery can retrieve zero or more rowsBOnly two subqueries can be placed atone levelCA subquery can be used only in SQL query statementsDA subquery can appear on either side of a comparison oper

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 are true about WHERE and HAVING clauses? （）

• A、A WHERE clause can be used to restrict both rows and groups.
• B、A WHERE clause can be used to restrict rows only.
• C、A HAVING clause can be used to restrict both rows and groups.
• D、A HAVING clause can be used to restrict groups only.
• E、A WHERE clause CANNOT be used in a query of the query uses a HAVING clause.
• F、A HAVING clause CANNOT be used in subqueries.

第3题：

第4题：

Which two statements regarding a SQL profile are true？（）

• A、 It is built by Automatic Tuning Optimizer.
• B、 It cannot be stored persistently in the data dictionary.
• C、 It can be used by the query optimizer automatically.
• D、 It can be created manually by using the CREATE PROFILE command.

第5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6题：

Which two statements are true regarding views?（）

• A、A subquery that defines a view cannot include the GROUP BY clause 
• B、A view that is created with the subquery having the DISTINCT keyword can be updated 
• C、A view that is created with the subquery having the pseudo column ROWNUM keyword cannot be updated 
• D、A data manipulation language (DML) operation can be performed on a view that is created with the subquery having all the NOT NULL columns of a table

第7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8题：

第9题：

Which three statements about subqueries are true?（）

• A、A single row subquery can retrieve only one column and one row.
• B、A single row subquery can retrieve only one row but many columns.
• C、A multiple row subquery can retrieve multiple rows and multiple columns.
• D、A multiple row subquery can be compared by using the ">" operator.
• E、A single row subquery can use the IN operator.
• F、A multiple row subquery can use the "=" operator.

第10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.