SQL Exercises: Customers along with the salesmen who works for them

Last update on March 27 2023 12:43:03 (UTC/GMT +8 hours)

SQL Query on Multiple Tables: Exercise-2 with Solution

From the following tables, write a SQL query to locate all the customers and the salesperson who works for them. Return customer name, and salesperson name.

Sample table: customer

Sample table: salesman

Sample Solution:

SELECT customer.cust_name, salesman.name
FROM customer,salesman
WHERE salesman.salesman_id = customer.salesman_id;

Output of the query:

cust_name	name
Nick Rimando	James Hoog
Brad Davis	James Hoog
Graham Zusi	Nail Knite
Julian Green	Nail Knite
Fabian Johnson	Mc Lyon
Geoff Cameron	Lauson Hen
Jozy Altidor	Paul Adam
Brad Guzan	Pit Alex

Code Explanation:

The given query in SQL that joins the 'customer' and 'salesman' tables based on the "salesman_id" column. The result set includes the customer name (cust_name) and salesman name (name). The WHERE clause specifies the join condition between the two tables, which is that the "salesman_id" column must be equal in both tables.

Relational Algebra Expression:

Relational Algebra Tree:

Explanation:

Syntax to find the names of all customers along with the salesmen who works for them

Visual presentation:

Result of the names of all customers along with the salesmen who works for them

Practice Online

Query Visualization:

Duration:

Rows:

Cost:

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Previous SQL Exercise: Customer and salesmen who lives in the same city.
Next SQL Exercise: Customer lives in a city other than the salesman's.

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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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