correct answerWhat is the SQL keyword used to specify that a column can contain NULL values?OptionsNOT NULLNULL ABLEALLOW NULLWITH NULLS

Breakdown the Problem

The question asks for the SQL keyword that indicates a column can have NULL values. It provides four options to choose from.

Relevant Concepts

In SQL, certain keywords are used to define the behavior of columns in terms of NULL values. The options provided are:

1. NOT NULL: This keyword specifies that a column cannot contain NULL values.
2. NULL: This is not an SQL keyword to define a column, but rather represents the absence of a value.
3. ABLE: This is not a valid SQL keyword.
4. ALLOW NULL: This is also not a standard SQL keyword.
5. WITH NULLS: This does not specify that a column can contain NULL values.

Analysis and Detail

• The correct keyword to specify that a column can contain NULL values is often implicit when defining a column without any constraints.
• The keyword NULL can be associated with the concept, but it is not used as an explicit constraint like NOT NULL.

Verify and Summarize

Among the options given, none are used specifically to declare a column as allowing NULL values. Generally, if a column is not declared with NOT NULL, it can accept NULL values by default.

Final Answer

The correct answer is: NULL (as a general concept; however, it’s typically inferred when not using NOT NULL).