What is the SQL keyword used to specify that a column can contain NULL values?OptionsALLOW NULLNOT NULLNULL ABLEWITH NULLS

Determining the Correct SQL Keyword

1. Understanding NULL Values in SQL
   In SQL, a column can be designed to either accept or not accept NULL values.

2. Exploration of Options

   • ALLOW NULL: This option does not exist in SQL syntax.
   • NOT NULL: This keyword is used to specify that a column cannot contain NULL values, which is the opposite.
   • NULL ABLE: This is not a recognized SQL keyword.
   • WITH NULLS: This also does not refer to a column specification in the context of NULL values.

3. Identifying the Correct Answer
   The keyword commonly used to specify that a column can contain NULL values is typically just the absence of NOT NULL. So, the concept that allows NULL values is simply implied unless specified otherwise.

Final Answer

The correct SQL keyword that indicates a column can contain NULL values is simply the absence of "NOT NULL." None of the provided options accurately express this concept.