SQL Exercise: Display the average price of items of each company

SQL JOINS: Exercise-23 with Solution

From the following tables write a SQL query to calculate the average price of items of each company. Return average value and company name.

Sample table: company_mast

COM_ID COM_NAME
------ -------------
    11 Samsung
    12 iBall
    13 Epsion
    14 Zebronics
    15 Asus
    16 Frontech

Sample table: item_mast

 PRO_ID PRO_NAME                       PRO_PRICE    PRO_COM
------- ------------------------- -------------- ----------
    101 Mother Board                    3200.00         15
    102 Key Board                        450.00         16
    103 ZIP drive                        250.00         14
    104 Speaker                          550.00         16
    105 Monitor                         5000.00         11
    106 DVD drive                        900.00         12
    107 CD drive                         800.00         12
    108 Printer                         2600.00         13
    109 Refill cartridge                 350.00         13
    110 Mouse                            250.00         12

Sample Solution:

-- Selecting the average of 'pro_price' and the company name from the result of an inner join between 'item_mast' and 'company_mast' tables
SELECT AVG(pro_price), company_mast.com_name
-- Specifying the tables to retrieve data from ('item_mast' as the left table and 'company_mast' as the right table)
FROM item_mast 
-- Performing an inner join based on the equality of 'pro_com' in 'item_mast' and 'com_id' in 'company_mast'
INNER JOIN company_mast
ON item_mast.pro_com = company_mast.com_id
-- Grouping the results by the company name
GROUP BY company_mast.com_name;

Output of the Query:

avg			com_name
5000.0000000000000000	Samsung
650.0000000000000000	iBall
1475.0000000000000000	Epsion
500.0000000000000000	Frontech
250.0000000000000000	Zebronics
3200.0000000000000000	Asus

Explanation:

The said SQL query is selecting the average price of all products (AVG(pro_price)) and the company name (com_name) from the tables item_mast and company_mast, and grouping the results by the company name.
The query is using an INNER JOIN to combine the data from the two tables, linking the 'pro_com' column in item_mast to the 'com_id' column in company_mast.

Relational Algebra Expression:

Relational Algebra Tree:

Practice Online

Query Visualization:

Duration:

Rows:

Cost:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous SQL Exercise: Display the item name, price, and company name.
Next SQL Exercise: Company whose products have an average price.