﻿ SQL - Display distinct salesman and their cities

# SQL Exercises: Display distinct salesman and their cities

## SQL UNION: Exercise-2 with Solution

2. From the following tables, write a SQL query to find distinct salespeople and their cities. Return salesperson ID and city.

Sample table: Salesman

Sample table: Customer

Sample Solution:

``````SELECT salesman_id, city
FROM customer
UNION
(SELECT salesman_id, city
FROM salesman)
``````

Sample Output:

```salesman_id	city
5001	    New York
5002	    London
5002	    California
5006	    Paris
5007	    Rome
5002	    Paris
5005	    London
5003	    Berlin
5007	    Moscow
5003	    San Jose
```

Code Explanation:

The said query in SQL that retrieves a list of unique pairs of salesman_id and city from two different tables, customer and salesman. The UNION operator is used to combine the results of two separate SELECT statements into a single result set.
The resulting table will contain all the unique combinations of salesman_id and city that appear in either the customer or salesman tables.

Relational Algebra Expression:

Relational Algebra Tree:

## Query Visualization:

Duration:

Rows:

Cost:

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Previous SQL Exercise: Display all salesmen and customer located in London.
Next SQL Exercise: Salesmen, customer involved in inventory management.

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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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