Revature Practice Test 2025 – Complete Exam Prep Guide

The major difference between HAVING and WHERE in SQL queries is that WHERE filters records before any aggregation occurs, while HAVING filters the results after aggregation has taken place. This distinction is crucial because it determines when each clause is applied during the data retrieval process.

The WHERE clause is typically used to specify conditions on individual rows of data in a database table. It is applied before any grouping or aggregation, so it helps narrow down the dataset right from the start. For example, if you want to filter out records that do not meet certain criteria, you would use WHERE.

On the other hand, HAVING is specifically designed to work with aggregated data. After the records have been grouped (usually with a GROUP BY clause), HAVING can apply conditions to these groups. This allows you to filter out the groups based on the results of aggregate functions (like SUM, AVG, COUNT, etc.) that are computed after the data has been grouped.

By understanding this distinction, one can effectively execute complex data queries that require both filtering individual records and applying conditions to aggregated data sets.