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

The primary purpose of a WHERE clause in SQL is to filter records before any groupings are applied. This means that the WHERE clause allows you to specify conditions that the rows must meet in order to be included in the result set of a query. By applying this filter at the beginning, it ensures that only relevant data is processed, which can lead to more efficient query execution and clearer results.

Using the WHERE clause effectively narrows down the output to only those records that fit the specified criteria, thereby enhancing data retrieval efficiency. The filtering occurs before any other operations, such as grouping or sorting, ensuring that only the desired subset of data is considered in subsequent steps of the query.