#Mysql count distinct group by how to#

Imagine an intermediate table where these rows are grouped and marked with different colors, like the image below. The rows with the same value in the Store column are grouped together. Let's break down the result to understand how this query works.

The correct way of using COUNT() with GROUP BY is shown in the query below: If you’re here just for the quick answer, here’s the TLDR:

It contains 129 exercises, which will help you review all key SQL concepts.

#Mysql count distinct group by how to#

In this tutorial, you have learned how to use the Oracle COUNT() function to return the number of items in a group.If you’re looking for an in-depth review of basic SQL concepts like COUNT() and GROUP BY, I recommend our interactive SQL Basics course. Finally, the HAVING clause returns only groups that have more than one value of the last name.Secondly, the COUNT() function returns the number of the same last names for each last name.Firstly, the GROUP BY clause divides the rows in the contacts table into groups based on the values in the last_name column.You can use the COUNT() function and a HAVING clause to find rows with duplicate values in a specified column.įor example, the following statement returns the contacts’ last names that appear more than one: SELECT SELECTĬode language: SQL (Structured Query Language) ( sql ) G) Using Oracle COUNT() and HAVING clause to find duplicate values In addition, it uses a HAVING clause to return the only category whose the number of products is greater than 50. The following statement retrieves category names and the number of products in each. SELECTĬode language: SQL (Structured Query Language) ( sql ) F) Oracle COUNT() with HAVING clause example The following examples get all category names and the number of products in each category by joining the product_categories with the products table and using the COUNT() function with the GROUP BY clause. Second, the COUNT(*) function returns the number of products for each group.First, the GROUP BY clause divides the products into groups based on the product category ( category_id).To find the number of products in each product category, you use the following statement: SELECT If you want to find the number of products in the category id 1, you can add a WHERE clause to the query above: SELECT COUNT(*)Ĭode language: SQL (Structured Query Language) ( sql ) D) Oracle COUNT() with GROUP BY clause example The following example returns the number of rows in the products table: SELECT COUNT(*)Ĭode language: SQL (Structured Query Language) ( sql ) C) Oracle COUNT() with WHERE clause example SELECT COUNT( ALL val )Ĭode language: SQL (Structured Query Language) ( sql ) B) Simple Oracle COUNT() example The following statement uses the COUNT(ALL val) function to return the number of non-null rows in the items table, considering duplicates. The following statement uses the COUNT(DISTINCT val) to return only the number of distinct and non-null rows from the items table: SELECT COUNT( DISTINCT val ) The following statement uses the COUNT(*) function to return the number of rows in the items table including NULL and duplicate values: SELECT COUNT(*) Let’s create a table named items that consists of a val column and insert some sample data into the table for the demonstration. Let’s take some examples of using the COUNT() function. Note that, unlike other aggregate functions such as AVG() and SUM(), the COUNT(*) function does not ignore NULL values. If you don’t explicitly specify DISTINCT or ALL, the COUNT() function uses the ALL by default. COUNT(ALL expression) evaluates the expression and returns the number of non-null items in a group, including duplicate values.COUNT(DISTINCT expression) function returns the number of unique and non-null items in a group.COUNT(*) function returns the number of items in a group, including NULL and duplicate values.The COUNT() function accepts a clause which can be either ALL, DISTINCT, or *: The syntax of the COUNT() function is as follows: COUNT( expression)Ĭode language: SQL (Structured Query Language) ( sql ) The Oracle COUNT() function is an aggregate function that returns the number of items in a group. Summary: in this tutorial, you will learn how to use the Oracle COUNT() function to get the number of items in a group.