sql select query using inner join - mysql

Question

I was wondering why my code isn't working. I'm trying to retrieve all offers of a listing only.
CREATE DATABASE IF NOT EXISTS `assignment_db`;
USE `assignment_db`;
CREATE TABLE USER_LIST(
id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
userName VARCHAR(50) NOT NULL,
email varchar(100) NOT NULL,
registeredDate timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
);
create table listing_list(
id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
itemName VARCHAR(50) NOT NULL,
itemDescription VARCHAR(254) NOT NULL,
price DECIMAL(4,2) NOT NULL,
fk_poster_id int references USER_LIST(id),
created_at timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
);
create table offer_list(
id int(6) Unsigned auto_increment Primary key,
offer int,
fk_listing_id int references listing_list(id),
fk_offeror_id int references user_list(id),
created_at timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
);
insert into user_list (userName, email) values ('John','johnnyboi#123.com');
insert into user_list (userName, email) values ('Tom','Tommyboi#123.com');
insert into listing_list (itemName,itemDescription, price) values ( 'Pen', 'A long delicate pen.',' 1.50 ');
insert into listing_list (itemName,itemDescription, price) values ( 'Pencil', 'A long delicate pencil.',' 0.50 ');
insert into offer_list (offer,fk_listing_id,fk_offeror_id) values ('200','2','3');
insert into offer_list (offer,fk_listing_id,fk_offeror_id) values ('200','1','1');
select * from listing_list
inner join offer_list on listing_list.fk_listing_id = offer_list.id;
Any ideas on how to resolve this?

Answer 1

If I've understood you correctly, you want something like this (see fiddle here). Note that I changed some of the numbers to make it easier to follow the flow of the query:
insert into user_list (id, userName, email) values (10, 'John','johnnyboi#123.com');
insert into user_list (id, userName, email) values (20, 'Tom','Tommyboi#123.com');
and
insert into listing_list (itemName,itemDescription, price, fk_poster_id)
values ( 'Pen', 'A long delicate pen.',' 1.50 ', 10);
insert into listing_list (itemName,itemDescription, price, fk_poster_id)
values ( 'Pencil', 'A long delicate pencil.',' 0.50 ', 20);
and
insert into offer_list (offer,fk_listing_id,fk_offeror_id)
values ('200','1', 10);
insert into offer_list (offer,fk_listing_id,fk_offeror_id)
values ('200','2', 20);
Then I ran the query:
SELECT
u.id,
u.username,
u.email,
l.id,
l.itemName,
l.itemDescription,l.price,
l.fk_poster_id,
l.created_at,
o.offer,
o.fk_listing_id
FROM user_list u
JOIN listing_list l ON u.id = l.fk_poster_id
JOIN offer_list o ON u.id = o.fk_offeror_id;
Result:
id username email id itemName itemDescription price fk_poster_id created_at offer fk_listing_id
10 John johnnyboi#123.com 1 Pen A long delicate pen. 1.50 10 2019-12-23 11:21:10 200 1
20 Tom Tommyboi#123.com 2 Pencil A long delicate pencil. 0.50 20 2019-12-23 11:21:10 200 2
Some of the result fields are redundant - I left them in so that you could see the reasoning. Can I recommend that in future a) you don't bother with backticks for MySQL anymore - they are no longer required and are a pain to type. Also, when dealing with numberic values - even though MySQL (weirdly) supports this, that you do not put numbers in single quotes - it makes the SQL more difficult to read using many SQL formatting tools.

Answer 2

select * from listing_list inner join offer_list on listing_list.id = offer_list.fk_listing_id
You have taken the wrong table names.
For more details, check https://www.w3schools.com/sql/sql_join_inner.asp
The basic syntax for inner join:
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;
If you want to select the data only form 1 listing, you can do it
like:
SELECT
*
FROM
listing_list
INNER JOIN offer_list ON listing_list.id = offer_list.fk_listing_id
WHERE
listing_list.id = 1