What is the primary purpose of a WHERE clause in SQL?

The primary purpose of a WHERE clause in SQL is to filter rows before any grouping occurs. This clause allows you to specify conditions that must be met for rows to be selected in the result set of a query. By applying the WHERE clause, you can refine your dataset based on specific criteria, such as matching certain column values, which directly impacts the data retrieved from the database.

When the WHERE clause is used, it processes the data first, ensuring that only the relevant rows are considered, which is particularly important in scenarios where aggregations (like summing or counting) may take place afterward. If you reach the aggregation stage before filtering, the results would be skewed or incorrect. Thus, the WHERE clause effectively sets the stage for any subsequent operations that may be performed on the data, such as GROUP BY or HAVING clauses that handle aggregations.

In contrast, using filtering after aggregation would require the HAVING clause, which operates on already aggregated data. The other options relate to different SQL functionalities, showing that the WHERE clause plays a critical role specifically in pre-aggregation scenarios.