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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

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Which two statements are true regarding single row functions?（）

A.They accept only a single argument
B.They can be nested only to two levels
C.Arguments can only be column values or constants
D.They always return a single result row for every row of a queried table
E.They can return a data type value different from the one that is referenced

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You need to generate a list of all customer last names with their credit limits from the CUSTOMERS table. Those customers who do not have a credit limit should appear last in the list. Which two queries would achieve the required result?（）

A.SELECT cust_last_name, cust_credit_limit FROM customers ORDER BY cust_credit_limit DESC
B.SELECT cust_last_name, cust_credit_limit FROM customers ORDER BY cust_credit_limit
C.SELECT cust_last_name, cust_credit_limit FROM customers ORDER BY cust_credit_limit NULLS LAST
D.SELECT cust_last_name, cust_credit_limit FROM customers ORDER BY cust_last_name, cust_credit_limit NULLSLAST

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Where can subqueries be used?（）

A.field names in the SELECT statement
B.the FROM clause in the SELECT statement
C.the HAVING clause in the SELECT statement
D.the GROUP BY clause in the SELECT statement
E.the WHERE clause in only the SELECT statement
F.the WHERE clause in SELECT as well as all DML statements