SQL Aggregation: Having vs Where Clause

Discussing the difference between where and having a clause with aggregate function

Introduction

• SQL provides different types of clauses such as where, having, like, etc. These clauses help us to filter data, perform aggregation and analyze the data.
• In this article, we will discuss where & having clauses along with aggregation function. We will also cover the difference between them.

Table

• I created a sample table called book_reviews for this tutorial which looks like below

Table description

• It contains basic columns for book reviews such as user_id, isbn, and rating.

postgres=# \d book_reviews
                                   Table "public.book_reviews"
   Column    |  Type   | Collation | Nullable |                     Default
-------------+---------+-----------+----------+--------------------------------------------------
 reviews_id  | integer |           | not null | nextval('book_reviews_reviews_id_seq'::regclass)
 user_id     | text    |           |          |
 isbn        | text    |           |          |
 book_rating | text    |           |          |
Indexes:
    "book_reviews_pkey" PRIMARY KEY, btree (reviews_id)