PROMO_CATEGORY NOT NULLVARCHAR2(30)

PROMO_COST NOT NULLNUMBER(10,2)

The management wants tosee a report of unique promotion costs in each promotion category.

Which query wouldachieve the required result

A. SELECT DISTINCTpromo_cost, promo_category FROM promotions;

B. SELECTpromo_category, DISTINCT promo_cost FROM promotions;

C. SELECT DISTINCTpromo_cost, DISTINCT promo_category FROM promotions;

D. SELECT DISTINCTpromo_category, promo_cost FROM promotions ORDER BY 1;

Answer: D

解析：distinct后的字段顺序不同，得到的结果顺序也不同，但是最终的内容都是一样的，所以A和D的差别主要是order by 1的区别，下面我们看看它的作用：

使用前：

scott@ORCL>selectdistinct job,sal from emp;

JOB SAL

--------- ----------

MANAGER 3324.24

SALESMAN 1600

SALESMAN 1250

CLERK 950

MANAGER 2450

ANALYST 3000

PRESIDENT 6300

ANALYST 1850

CLERK 1100

MANAGER 2975

SALESMAN 1500

CLERK 1430

已选择12行。

使用后：

scott@ORCL>selectdistinct job,sal from emp order by 1;

JOB SAL

--------- ----------

ANALYST 1850

ANALYST 3000

CLERK 950

CLERK 1100

CLERK 1430

MANAGER 2450

MANAGER 2975

MANAGER 3324.24

PRESIDENT 6300

SALESMAN 1250

SALESMAN 1500

SALESMAN 1600

已选择12行。

根据题意这里选择D选项更佳

19. eva luate thefollowing query:

SELECT INTERVAL '300'MONTH,

INTERVAL '54-2' YEAR TOMONTH,

INTERVAL'11:12:10.1234567' HOUR TO SECOND

FROM dual;

What is the correctoutput of the above query

A. +25-00 , +54-02, +0011:12:10.123457

B. +00-300, +54-02, +0011:12:10.123457

C. +25-00 , +00-650, +0011:12:10.123457

D. +00-300 , +00-650,+00 11:12:10.123457

Answer: A

解析：

scott@ORCL>SELECTINTERVAL '300' MONTH,

2 INTERVAL '54-2' YEAR TO MONTH,

3 INTERVAL '11:12:10.1234567' HOURTO SECOND

4 FROMdual;

INTERVAL'300'MONTH INTERVAL'54-2'YEARTOMONTH INTERVAL'11:12:10.1234567'HOURTOSECOND

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

+25-00 +54-02 +00 11:12:10.123457

scott@ORCL>

官方文档：

INTERVAL YEAR TO MONTHData Type

INTERVAL YEAR TO MONTHstores a period of time using the YEAR and MONTH

datetime fields. Thisdata type is useful for representing the difference between two

datetime values whenonly the year and month values are significant.

Specify INTERVAL YEAR TOMONTH as follows:

INTERVAL YEAR[(year_precision)] TO MONTH

where year_precision isthe number of digits in the YEAR datetime field. The

default value ofyear_precision is 2.

引用网友：

由于MONTH 默认是2为有效位数，所以不能是300，就表示成YEAR TO MONTH 于是成了+25-00

第二个不够2位补0，第三个最后一位默认6位，收上来就是123457了

20. Which threestatements are true regarding the data types in Oracle Database 10g/11g (Choose

three.)

A. Only one LONG columncan be used per table.

B. A TIMESTAMP data typecolumn stores only time values with fractional seconds.

C. The BLOB data typecolumn is used to store binary data in an operating system file.

D. The minimum columnwidth that can be specified for a VARCHAR2 data type column is one.

E. The value for a CHARdata type column is blank-padded to the maximum defined column width.

Answer: ADE

解析：
引用oracle官方文档：
The use of LONG values is subject to these restrictions:

■ A table can contain only one LONG column.

■ You cannot create anobject type with a LONG attribute.

■ LONG columns cannotappear in WHERE clauses or in integrity constraints (except

that they can appear inNULL and NOT NULL constraints).

……….