Difference Between WHERE and HAVING Clauses in PostgreSQL Queries

When writing PostgreSQL queries, it is important to understand the distinction between the WHERE and HAVING clauses.

The WHERE clause is used to filter rows based on specified conditions on columns before any groupings are made. It is a part of the SELECT statement and is applied before any GROUP BY clause. The WHERE clause is typically used to filter individual rows based on certain criteria.

On the other hand, the HAVING clause is used to filter rows that are the result of aggregate functions like SUM, AVG, COUNT, etc. It is applied after the GROUP BY clause and is used to filter grouped rows based on specified conditions.

In summary, while the WHERE clause filters individual rows based on conditions, the HAVING clause filters grouped rows based on aggregate function results.

Understanding the difference between the WHERE and HAVING clauses in PostgreSQL queries is crucial for writing efficient and effective SQL queries.