﻿ SQL: Company whose products have an average price

# SQL Exercise: Company whose products have an average price

## SQL JOINS: Exercise-24 with Solution

From the following tables write a SQL query to calculate and find the average price of items of each company higher than or equal to Rs. 350. Return average value and company name.

Sample table: company_mast

Sample table: item_mast

Sample Solution:

`````` SELECT AVG(pro_price), company_mast.com_name
FROM item_mast INNER JOIN company_mast
ON item_mast.pro_com= company_mast.com_id
GROUP BY company_mast.com_name
HAVING AVG(pro_price) >= 350;
``````

Output of the Query:

```          avg          | com_name
-----------------------+----------
5000.0000000000000000 | Samsung
650.0000000000000000 | iBall
1475.0000000000000000 | Epsion
500.0000000000000000 | Frontech
3200.0000000000000000 | Asus
(5 rows)
```

Explanation:

The said SQL query is selecting the average price (AVG(pro_price)) of items and the name of the company (company_mast.com_name) they are associated with, by joining the item_mast and company_mast tables on the pro_com column in the item_mast table and the com_id column in the company_mast table. The results are grouped by the company name and only showing the results where the average price is greater than or equal to 350.

Relational Algebra Expression:

Relational Algebra Tree:

## Query Visualization:

Duration:

Rows:

Cost:

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Previous SQL Exercise: Display the average price of items of each company.
Next SQL Exercise: Display ID and price of most expensive product.

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## SQL: Tips of the Day

Grouped LIMIT in PostgreSQL: Show the first N rows for each group?

```db=# SELECT * FROM xxx;
id | section_id | name
----+------------+------
1 |          1 | A
2 |          1 | B
3 |          1 | C
4 |          1 | D
5 |          2 | E
6 |          2 | F
7 |          3 | G
8 |          2 | H
(8 rows)
```

I need the first 2 rows (ordered by name) for each section_id, i.e. a result similar to:

```id | section_id | name
----+------------+------
1 |          1 | A
2 |          1 | B
5 |          2 | E
6 |          2 | F
7 |          3 | G
(5 rows)
```

PostgreSQL v9.3 you can do a lateral join

```select distinct t_outer.section_id, t_top.id, t_top.name from t t_outer
join lateral (
select * from t t_inner
where t_inner.section_id = t_outer.section_id
order by t_inner.name
limit 2
) t_top on true
order by t_outer.section_id;
```

Database: PostgreSQL

Ref: https://bit.ly/3AfYwZI

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