SQL Exercises: Find out customers who made the order

Last update on March 27 2023 12:42:37 (UTC/GMT +8 hours)

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

Sample table: customer

Sample Solution:

SELECT orders.ord_no, customer.cust_name
FROM orders, customer
WHERE orders.customer_id = customer.customer_id;

Output of the query:

ord_no	cust_name
70009	Brad Guzan
70002	Nick Rimando
70004	Geoff Cameron
70005	Brad Davis
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:

Syntax to find out customers who made the order

Visual presentation :

Practice Online

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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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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