When is it appropriate to use a WHERE clause in SQL?

The WHERE clause in SQL is primarily used to filter results based on specific conditions within a query. It allows you to refine the results returned from a SELECT statement, ensuring that only the rows meeting certain criteria are included in the output. For example, if you have a table of customers and you want to see only those who live in a particular city, you can specify that condition using a WHERE clause.

This functionality is crucial when working with databases because it enables querying of a subset of data, rather than retrieving all available records, which may be unmanageable and unnecessary for analysis or reporting. Thus, its primary role is to limit the result set and focus on particular data points of interest.