To answer this question, you need to understand the concept of check constraints in Oracle.
Check constraints in Oracle allow you to define a condition that must be true for each row in a table. This condition is specified as an expression, and it can reference multiple columns in the table. The purpose of a check constraint is to ensure that the data in the table meets certain criteria.
Let's go through each option to understand why it is correct or incorrect:
Option A) Values must be obtained from a lookup table.
This option is incorrect because check constraints in Oracle do not require values to be obtained from a lookup table. The values can be any valid expression that evaluates to true or false.
Option B) Values must be part of a fixed set defined by create or alter table.
This option is correct. Check constraints in Oracle can be used to enforce that the values in a column must be part of a fixed set defined by the create or alter table statement. This means that the values must be explicitly specified and cannot be any arbitrary values.
Option C) Values must include reserved words, such as SYSDATE and USER.
This option is incorrect. Check constraints in Oracle do not require values to include reserved words. The values can be any valid expression that evaluates to true or false.
Option D) The column cannot contain a NULL value.
This option is incorrect. Check constraints in Oracle can allow NULL values in a column. Whether or not NULL values are allowed is determined by the NULL or NOT NULL constraint, not the check constraint.
The correct answer is B) Values must be part of a fixed set defined by create or alter table. This option is correct because it accurately describes one of the limitations on check constraints in Oracle.