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

The purpose of the WHERE clause in a SQL query is to set criteria for returning records. This clause allows you to filter results based on specific conditions, ensuring that only the rows that meet those criteria are included in the result set. For example, if you're querying a database for employees, you might want to return only those who work in a particular department or have a certain job title. By using the WHERE clause, you can define these conditions, allowing for more precise and relevant data retrieval.

Setting criteria is crucial in database querying because it optimizes performance and relevance, particularly when dealing with large datasets. Without the WHERE clause, a query would return all records from a table, which may not be useful or efficient. Thus, the WHERE clause enhances the query's effectiveness by narrowing down the results to what is specifically needed.