OCP-1Z0-051-题目解析-第21题

21. Examine the description of the EMP_DETAILS table given below:

name               NULL                 TYPE

EMP_ID             NOT NULL             NUMBER

EMP_NAME           NOT NULL             VARCHAR2 (40)

EMP_IMAGE                               LONG

Which two statements are true regarding SQL statements that can be executed on the EMP_DETAIL table?

(Choose two.)

A. An EMP_IMAGE column can be included in the GROUP BY clause.

B. An EMP_IMAGE column cannot be included in the ORDER BY clause.

C. You cannot add a  new column to the table with LONG as the  data type.

D. You can alter the table to include the  NOT NULL constraint on the EMP_IMAGE column.

Answer: BC

关于long类型的字段有下面特点：

1: 在Group By 和Order By 字句中不能包括含有long类型的字段。

2: 使用子查询建表的时候不复制含有long类型的字段。

3: 不能对long类型的字段定义约束条件

4: 一个表仅仅能含有一个long类型的字段

A: EMP_IMAGE字段能够被包括在Group By 子句中（错误，EMP_IMAGE的类型是long）

B: EMP_IMAGE字段不能够包括在Order By 子句中（正确）

C: 不能再向表中加入一个数据类型是long的新字段 （正确，表中已含有long类型的字段）

D: 能够更新表，加入not null约束到EMP_IMAGE字段中（错误。long类型的字段不能加入不论什么约束）

时间： 2024-10-30 09:19:54

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