﻿ SQL - Any salesman was matched to the city of any customer

# SQL Exercises: Any salesman was matched to the city of any customer

## SQL UNION : Exercise-7 with Solution

7. From the following tables, write a SQL query that appends strings to the selected fields, indicating whether the city of any salesperson is matched with the city of any customer. Return salesperson ID, name, city, MATCHED/NO MATCH.

Sample table: Salesman

Sample table: Customer

Sample Solution:

``````SELECT a.salesman_id, name, a.city, 'MATCHED'
FROM salesman a, customer b
WHERE a.city = b.city
UNION
(SELECT salesman_id, name, city, 'NO MATCH'
FROM salesman
WHERE NOT city = ANY
(SELECT city
FROM customer))
ORDER BY 2 DESC
``````

Sample Output:

```salesman_id	name		city		?column?
5005		Pit Alex	London		MATCHED
5007		Paul Adam	Rome		NO MATCH
5002		Nail Knite	Paris		MATCHED
5006		Mc Lyon		Paris		MATCHED
5003		Lauson Hen	San Jose	NO MATCH
5001		James Hoog	New York	MATCHED
```

Code Explanation:

The said query in that retrieves information about salesmen and their cities, and whether or not they have customers in the same city.
The result set includes salesmen who have customers in their city, as well as salesmen who do not have customers in any city. The result set is sorted by the salesmen's names in descending order.
The uses of JOIN clause between the salesman and customer tables retrieve all salesmen who have customers in the same city. The SELECT statement also adds a column with the value 'MATCHED' to indicate that these salesmen have a match with a customer.
The second part of the query uses a subquery to retrieve all salesmen who do not have customers in any city. The SELECT statement also adds a column with the value 'NO MATCH' to indicate that these salesmen do not have a match with a customer.
The UNION operator combines the results of the two queries into a single result set.
The ORDER BY clause sorts the result set by the second column in descending order i.e., by the salesmen's names.

## Query Visualization:

Duration:

Rows:

Cost:

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Previous SQL Exercise: Salesmen who do not have customers in their cities.
Next SQL Exercise: Ratings of all customers with a comment string.

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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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