﻿ SQL - Find out customers who made the order

# SQL Exercises: Find out customers who made the order

## SQL Query on Multiple Tables: Exercise-4 with Solution

From the following tables, write a SQL query to locate the orders made by customers. Return order number, customer name.

Sample table: orders

```ord_no      purch_amt   ord_date    customer_id  salesman_id
----------  ----------  ----------  -----------  -----------
70001       150.5       2012-10-05  3005         5002
70009       270.65      2012-09-10  3001         5005
70002       65.26       2012-10-05  3002         5001
70004       110.5       2012-08-17  3009         5003
70007       948.5       2012-09-10  3005         5002
70005       2400.6      2012-07-27  3007         5001
70008       5760        2012-09-10  3002         5001
70010       1983.43     2012-10-10  3004         5006
70003       2480.4      2012-10-10  3009         5003
70012       250.45      2012-06-27  3008         5002
70011       75.29       2012-08-17  3003         5007
70013       3045.6      2012-04-25  3002         5001
```

Sample table: customer

``` customer_id |   cust_name    |    city    | grade | salesman_id
-------------+----------------+------------+-------+-------------
3002 | Nick Rimando   | New York   |   100 |        5001
3007 | Brad Davis     | New York   |   200 |        5001
3005 | Graham Zusi    | California |   200 |        5002
3008 | Julian Green   | London     |   300 |        5002
3004 | Fabian Johnson | Paris      |   300 |        5006
3009 | Geoff Cameron  | Berlin     |   100 |        5003
3003 | Jozy Altidor   | Moscow     |   200 |        5007
3001 | Brad Guzan     | London     |       |        5005
```

Sample Solution:

``````-- This query selects specific columns ('orders.ord_no' and 'customer.cust_name') from the 'orders' and 'customer' tables.
-- It retrieves data where the 'customer_id' column in the 'orders' table matches the 'customer_id' column in the 'customer' table.
SELECT orders.ord_no, customer.cust_name
-- Specifies the tables from which to retrieve the data (in this case, 'orders' and 'customer').
FROM orders, customer
-- Specifies the condition for joining the 'orders' and 'customer' tables based on the equality of the 'customer_id' columns.
WHERE orders.customer_id = customer.customer_id;
``````

Output of the query:

```ord_no	cust_name
70002	Nick Rimando
70004	Geoff Cameron
70008	Nick Rimando
70010	Fabian Johnson
70003	Geoff Cameron
70011	Jozy Altidor
70013	Nick Rimando
70001	Graham Zusi
70007	Graham Zusi
70012	Julian Green
```

Code Explanation:

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

Relational Algebra Expression:

Relational Algebra Tree:

Explanation:

Visual presentation :

## Query Visualization:

Duration:

Rows:

Cost:

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Previous SQL Exercise: Customer lives in a city other than the salesman's.
Next SQL Exercise: Sort out the customer who made at least an order.

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