27.Which two statements are true regarding tables?

27.Which two statements are true regarding tables?

A.A table name can be of any length.

B.A table can have any number of columns.

C.A column that has a DEFAULT value cannot store null values.

D.A table and a view can have the same name in the same schema.

E.A table and a synonym can have the same name in the same schema.

F.The same table name can be used in different schemas in the same database.

答案：如果必须选择两个的话那就EF

解析：

A：表名只能30个字符

B：列最大1000个

drop table test purge;
create table test (a0 number);
declare
v_sql varchar(100);
v_col varchar2(5);
begin
for i in 1 .. 10000 loop
v_col := 'a'||to_char(i);
v_sql := 'alter table test add( '||v_col||' char(1))';
execute immediate v_sql;
end loop;
exception
when others then
dbms_output.put_line(sqlerrm);
end;

输出：ORA-01792: 表或视图中的最大列数为 1000

select count(*) from user_tab_columns where table_name='TEST';

输出：1000

C：列可不可以存储null与默认值没有关系，与not null 约束有关系

D：表和视图不能相同的名字在同一个schema

create table test (a number);
create view test as select * from tab;

提示：ORA-00955: 名称已由现有对象使用

--那么临时表是否可以与视图同名

create global temporary table test1(a number) on commit delete rows;
create view test1 as select * from tab;

提示：ORA-00955: 名称已由现有对象使用

E:public 同义词可以和表同名

create table test (a number);
create synonym test for tab;

提示：ORA-00955: 名称已由现有对象使用

--创建public 同义词

create public synonym test for tab;

--这里成功了，所以如果是同名的话只能是public 同义词

F:正确