In database systems such as SQL, a wildcard character used in a WHERE clause pattern can match multiple possible values. In which of the following situations is using a wildcard in a WHERE clause particularly useful?

Introduction / Context:
This question relates to basic SQL and database concepts. Wildcard characters such as percent and underscore are often used in WHERE clauses in SELECT statements to match patterns rather than exact values. The question asks when such wildcards are most useful, and the options contrast SELECT and CREATE statements and exact versus inexact matches. Understanding the typical use of the LIKE operator and wildcards is the key to answering this question correctly.

Given Data / Assumptions:

• In SQL, the WHERE clause is used to filter rows returned by SELECT queries or, less commonly, to filter rows for UPDATE and DELETE.
• Wildcards are used with pattern matching operators such as LIKE.
• Wildcards help match unknown or variable portions of string values.
• CREATE statements are used to create tables, indexes, or databases, not to filter rows.
• The question specifically refers to a wildcard in a WHERE clause.

Concept / Approach:
A wildcard represents one or more unspecified characters in a pattern. In SQL, you normally use wildcards with LIKE in a SELECT statement when you only know part of a value or when you need to match a range of values that share some pattern. In CREATE statements, you define structure and do not filter data, so wildcards make no sense there. Similarly, when an exact match is required in a WHERE clause, wildcards are unnecessary. Therefore we look for the option that describes pattern based matching in a SELECT statement when the exact value is not fully known.

Step-by-Step Solution:
Step 1: Recall the syntax. A typical pattern matching query is SELECT * FROM customers WHERE name LIKE 'A%'; where percent is a wildcard for any sequence of characters.Step 2: Recognise the use case. We use such patterns when we do not know the full exact string, or when we want to match all values that start with, end with, or contain a certain substring.Step 3: Examine option a. It states that a wildcard in a WHERE clause is useful when an exact match is not possible in a SELECT statement and a pattern is needed. This matches the standard use of LIKE with wildcards.Step 4: Examine options b and c. They discuss CREATE statements, which do not use WHERE clauses to filter data values, so wildcards are irrelevant there.Step 5: Examine option d. It claims a wildcard is useful when an exact match is strictly necessary in SELECT, which is the opposite of how wildcards are used.Step 6: Option e claims wildcards are useful when no condition is required in the WHERE clause, which contradicts the idea of using a WHERE clause at all.

Verification / Alternative check:
Consider a realistic situation where a user wants all records where the product code begins with the letters CA but may have different numbers afterward. Using a WHERE clause with code LIKE 'CA%' is a textbook example of wildcard usage in a SELECT statement when you cannot or do not want to specify complete exact codes. This scenario matches option a precisely and confirms that the main role of wildcards is for partial or pattern based matches in SELECT queries.

Why Other Options Are Wrong:

• Options b and c refer to CREATE statements, which are for defining structures and do not use WHERE pattern matching on data.
• Option d claims wildcards are useful when exact matches are mandatory, which misrepresents their purpose.
• Option e is incorrect because if no condition is needed, the WHERE clause itself can be omitted, and wildcards have no role.

Common Pitfalls:
Students sometimes confuse the roles of different SQL statements and might think of wildcards as general features that can appear anywhere. It is important to remember that wildcards typically appear with LIKE in WHERE clauses of SELECT, UPDATE, or DELETE statements, and are rarely meaningful in CREATE statements. Another mistake is to think wildcards can improve exact matching; in fact, they are specifically for inexact or pattern based matching scenarios.

Final Answer:
When an exact match is not possible or not known in a SELECT statement and we need to match a pattern instead.