69. 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? (Choose two.)
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 NULLS LAST;
Answer: BC
答案解析：
对于升序排序，空值显示在最后，对于降序排序，则显示在最前面
who do not have a credit limit should appear last in the list
题目要求空值在最后面
要么升序排列，要么指定nulls last
D先按照cust_last_name排序，在按照 cust_credit_limit空值最后排序，不符合题意。
实验验证：
B,
scott@TESTDB> select * from emp order by comm;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7788 SCOTT ANALYST 7566 19-APR-87 3000 20
7839 KING PRESIDENT 17-NOV-81 5000 10
7876 ADAMS CLERK 7788 23-MAY-87 1100 20
C,
scott@TESTDB> select * from emp order by comm nulls last;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7788 SCOTT ANALYST 7566 19-APR-87 3000 20
7839 KING PRESIDENT 17-NOV-81 5000 10
7876 ADAMS CLERK 7788 23-MAY-87 1100 20
14 rows selected.
D,
scott@TESTDB> select * from emp order by ename,comm nulls last;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7876 ADAMS CLERK 7788 23-MAY-87 1100 20
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7698 BLAKE MANAGER 7839 01-MAY-81 2850 30
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
14 rows selected.