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SQL Exercise: Salesmen work for one or more customers or yet to join

SQL JOINS: Exercise-14 with Solution

Write a SQL statement to make a list for the salesmen who either work for one or more customers or yet to join any of the customer. The customer, may have placed, either one or more orders on or above order amount 2000 and must have a grade, or he may not have placed any order to the associated supplier.

Sample table: customer


Sample table: salesman


Sample table: orders


Sample Solution:

SELECT a.cust_name,a.city,a.grade, 
b.name AS "Salesman", 
c.ord_no, c.ord_date, c.purch_amt 
FROM customer a 
RIGHT OUTER JOIN salesman b 
ON b.salesman_id=a.salesman_id 
LEFT OUTER JOIN orders c 
ON c.customer_id=a.customer_id 
WHERE c.purch_amt>=2000 
AND a.grade IS NOT NULL;

Output of the Query:

cust_name     |city      |grade|Salesman  |ord_no|ord_date  |purch_amt|
--------------|----------|-----|----------|------|----------|---------|
Nick Rimando  |New York  |  100|James Hoog| 70002|2012-10-05|    65.26|
Geoff Cameron |Berlin    |  100|Lauson Hen| 70004|2012-08-17|   110.50|
Brad Davis    |New York  |  200|James Hoog| 70005|2012-07-27|  2400.60|
Nick Rimando  |New York  |  100|James Hoog| 70008|2012-09-10|  5760.00|
Fabian Johnson|Paris     |  300|Mc Lyon   | 70010|2012-10-10|  1983.43|
Geoff Cameron |Berlin    |  100|Lauson Hen| 70003|2012-10-10|  2480.40|
Jozy Altidor  |Moscow    |  200|Paul Adam | 70011|2012-08-17|    75.29|
Nick Rimando  |New York  |  100|James Hoog| 70013|2012-04-25|  3045.60|
Graham Zusi   |California|  200|Nail Knite| 70001|2012-10-05|   150.50|
Graham Zusi   |California|  200|Nail Knite| 70007|2012-09-10|   948.50|
Julian Green  |London    |  300|Nail Knite| 70012|2012-06-27|   250.45|

Explanation:

The said SQL query that is joining three tables: customer alias a, salesman alias b, and orders alias c. The query is using a RIGHT OUTER JOIN on salesman and customer tables on the 'salesman_id' column, and a LEFT OUTER JOIN on orders and customer tables on the 'customer_id' column.
The query is then selecting several columns from each table: 'cust_name', 'city', 'grade' from 'customer' table, 'name' aliased as 'Salesman' from salesman table, 'ord_no', 'ord_date', 'purch_amt' from orders table.
The query is also filtering the results based on the condition "c.purch_amt >=2000" and "a.grade IS NOT NULL" which means it will only return the rows where the purchase amount is greater than or equal to 2000 and grade is not null.

Visual Explanation:

Result of a list for the salesmen who either work for one or more customer or yet to join any of the customer
Result of a list for the salesmen who either work for one or more customer or yet to join any of the customer

Practice Online


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Previous SQL Exercise: Salesmen who works either for one or more customer.
Next SQL Exercise: One or more customers ordered from the existing list

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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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