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
關於long類型的欄位有以下特點:
1: 在Group By 和Order By 字句中不能包含含有long類型的欄位。
2: 使用子查詢建表的時候不複製含有long類型的欄位。
3: 不能對long類型的欄位定義約束條件
4: 一個表只能含有一個long類型的欄位
A: EMP_IMAGE欄位可以被包含在Group By 子句中(錯誤,EMP_IMAGE的類型是long)
B: EMP_IMAGE欄位不可以包含在Order By 子句中(正確)
C: 不能再向表中添加一個資料類型是long的新欄位 (正確,表中已含有long類型的欄位)
D: 可以更新表,添加not null約束到EMP_IMAGE欄位中(錯誤,long類型的欄位不能添加任何約束)