I have 3 tables with data, and I would like to create a report which shows me people with their books and furniture. The biggest problem is to get an independent list with two columns: books and furniture.
create table people (id int primary key)
create table books (id int primary key
, personId int foreign key references people(id))
create table furnitures (id int primary key
, personId int foreign key references people(id))
go
insert into people(id)
values (1),(2),(3)
insert into books(id,personId)
values (1,1),(2,1),(3,1),(4,1),(5,1),(6,3),(7,3)
insert into furnitures(id,personId)
values (1,2),(2,2),(3,2),(4,3),(5,3),(6,3),(7,3),(8,3)
I want to get a report in this form:
You need to do a join but you don't have a key. So, let's create one using row_number(). The rest is just a full outer join to combine the data:
select coalesce(b.personId, f.personId) as personId, b.id as bookid, f.id as furnitureid
from (select b.*, row_number() over (partition by personId order by id) as seqnum
from books b
) b
full join
(select f.*, row_number() over (partition by personId order by id) as seqnum
from furnitures f
) f
on f.personId = b.personId and b.seqnum = f.seqnum;
Related
I have two tables
create table AUTHORS
(
id integer primary key,
name varchar(30)
)
create table BOOKS
(
id integer primary key,
name varchar(30),
year integer,
sold_copies integer,
author_id integer references AUTHORS (id)
)
How would I create a table with authors in descending order per sold copies of books per year in pgAdmin4 (PostgreSQL) ?
im a beginner and I am not sure how to go about this
I don't see why you would need to create a new table. A simple SELECT will do (maybe stored inside a view)
select a.id, a.name, b.year, sum(b.sold_copies) as total_copies
from author a
join books b on b.author_id = a.id
group by a.id, a.name, b.year
order by sum(b.sold_copies) desc;
I have these Postgres tables:
create table deals_new
(
id bigserial primary key,
slip_id text,
deal_type integer,
timestamp timestamp,
employee_id bigint
constraint employee_id_fk
references common.employees
);
create table twap
(
id bigserial primary key,
deal_id varchar not null,
employee_id bigint
constraint fk_twap__employee_id
references common.employees,
status integer
);
create table employees
(
id bigint primary key,
account_id integer,
first_name varchar(150),
last_name varchar(150)
);
New table to query:
create table accounts
(
id bigint primary key,
account_name varchar(150) not null
);
I use this SQL query:
select d.*, t.id as twap_id
from common.deals_new d
left outer join common.twap t on
t.deal_id = d.slip_id and
d.timestamp between '11-11-2021' AND '11-11-2021' and
d.deal_type in (1, 2) and
d.quote_id is null
where d.employee_id is not null
order by d.timestamp desc, d.id
offset 10
limit 10;
How I can extend this SQL query to search also in table employees by account_id and map the result in table accounts by id? I would like to print also accounts. account_name based on employees .account_id.
You need two joins to to make this work for you. One join to get to the employee table, and one more join to get to the accounts table.
select d.*, t.id as twap_id, a.account_name
from common.deals_new d
left outer join common.twap t on
t.deal_id = d.slip_id and
d.timestamp between '11-11-2021' AND '11-11-2021' and
d.deal_type in (1, 2) and
d.quote_id is null
join employees as e on d.employee_id = e.id
join accounts as a on a.id = e.account_id
where d.employee_id is not null
order by d.timestamp desc, d.id
offset 10
limit 10;
Note: I did not fiddle this one, so could have a typo, but I think you get the idea here.
I am trying to join reviews and likes onto products, but it seems, for some reason that the output of "reviews" column is duplicated by the length of another foreign table, likes, the output length of "reviews" is
amount of likes * amount of reviews
I have no idea why this is happening
My desired output is that the "reviews" column contains an array of JSON data such that one array is equal to one row of a related review
Products
Title Image
----------------------
Photo photo.jpg
Book book.jpg
Table table.jpg
Users
Username
--------
Admin
John
Jane
Product Likes
product_id user_id
---------------------
1 1
1 2
2 1
2 3
Product Reviews
product_id user_id review
-------------------------------------
1 1 Great Product!
1 2 Looks Great
2 1 Could be better
This is the query
SELECT "products".*,
array_to_json(array_agg("product_review".*)) as reviews,
EXISTS(SELECT * FROM product_like lk
JOIN users u ON u.id = "lk"."user_id" WHERE u.id = 4
AND "lk"."product_id" = products.id) AS liked,
COUNT("product_like"."product_id") AS totalLikes from "products"
LEFT JOIN "product_review" on "product_review"."product_id" = "products"."id"
LEFT JOIN "product_like" on "product_like"."product_id" = "products"."id"
group by "products"."id"
Query to create schema and insert data
CREATE TABLE products
(id SERIAL, title varchar(50), image varchar(50), PRIMARY KEY(id))
;
CREATE TABLE users
(id SERIAL, username varchar(50), PRIMARY KEY(id))
;
INSERT INTO products
(title,image)
VALUES
('Photo', 'photo.jpg'),
('Book', 'book.jpg'),
('Table', 'table.jpg')
;
INSERT INTO users
(username)
VALUES
('Admin'),
('John'),
('Jane')
;
CREATE TABLE product_review
(id SERIAL, product_id int NOT NULL, user_id int NOT NULL, review varchar(50), PRIMARY KEY(id), FOREIGN KEY (product_id) references products, FOREIGN KEY (user_id) references users)
;
INSERT INTO product_review
(product_id, user_id, review)
VALUES
(1, 1, 'Great Product!'),
(1, 2, 'Looks Great'),
(2, 1, 'Could be better')
;
CREATE TABLE product_like
(id SERIAL, product_id int NOT NULL, user_id int NOT NULL, PRIMARY KEY(id), FOREIGN KEY (product_id) references products, FOREIGN KEY (user_id) references users)
;
INSERT INTO product_like
(product_id, user_id)
VALUES
(1, 1),
(1, 2),
(2, 1),
(2, 3)
fiddle with the schema and query:
http://sqlfiddle.com/#!15/dff2c/1
Thanks in advance
The reason you are getting multiple results is because of the one-to-many relationships between product_id and product_review and product_like causing duplication of rows prior to aggregation. To work around that, you need to perform the aggregation of those tables in subqueries and join the derived tables instead:
SELECT "products".*,
"pr"."reviews",
EXISTS(SELECT * FROM product_like lk
JOIN users u ON u.id = "lk"."user_id" WHERE u.id = 4
AND "lk"."product_id" = products.id) AS liked,
COALESCE("pl"."totalLikes", 0) AS totalLikes
FROM "products"
LEFT JOIN (SELECT product_id, array_to_json(array_agg("product_review".*)) AS reviews
FROM "product_review"
GROUP BY product_id) "pr" on "pr"."product_id" = "products"."id"
LEFT JOIN (SELECT product_id, COUNT(*) AS "totalLikes"
FROM "product_like"
GROUP BY product_id) "pl" on "pl"."product_id" = "products"."id"
Output:
id title image reviews liked totallikes
1 Photo photo.jpg [{"id":1,"product_id":1,"user_id":1,"review":"Great Product!"},{"id":2,"product_id":1,"user_id":2,"review":"Looks Great"}] f 2
2 Book book.jpg [{"id":3,"product_id":2,"user_id":1,"review":"Could be better"}] f 2
3 Table table.jpg f 0
Demo on dbfiddle
I have three tables: groups and people and groups_people which forms a many-to-many relationship between groups and people.
Schema:
CREATE TABLE groups (
id SERIAL PRIMARY KEY,
name TEXT
);
CREATE TABLE people (
id SERIAL PRIMARY KEY,
name TEXT,
join_date TIMESTAMP
);
CREATE TABLE groups_people (
group_id INT REFERENCES groups(id),
person_id INT REFERENCES people(id)
);
When I want to query for the latest 10 people who recenlty joined the group which has id = 1:
WITH person_ids AS (SELECT person_id FROM groups_people WHERE group_id = 1)
SELECT * FROM people WHERE id = ANY(SELECT person_id FROM person_ids)
ORDER BY join_date DESC LIMIT 10;
The query needs to scan all of the joined people then ordering them before selecting. That would be slow if the group containing too many people.
Is there anyway to work around it?
Schema (re-)design to allow same person joining multiple group
Since you mentioned that the relationship between groups and people
is many-to-many, I think you may want to move join_date to groups_people
(from people) because the same person can join different groups and each
such event has its own join_date
So I would change the schema to
CREATE TABLE people (
id SERIAL PRIMARY KEY,
name TEXT --, -- change
-- join_date TIMESTAMP -- delete
);
CREATE TABLE groups_people (
group_id INT REFERENCES groups(id),
person_id INT REFERENCES people(id), -- change
join_date TIMESTAMP -- add
);
Query
select
p.id
, p.name
, gp.join_date
from
people as p
, groups_people as gp
where
p.id = gp.person_id
and gp.group_id=1
order by gp.join_date desc
limit 10
Disclaimer: The above query is in MySQL syntax (the question was originally tagged with MySQL)
This seems much easier to write as a simple join with order by and limit:
select p.*
from people p join
groups_people gp
on p.id = gp.person_id
where gp.group_id = 1
order by gp.join_date desc
limit 10; -- or fetch first 10 rows only
Try rewriting using EXISTS
SELECT *
FROM people p
WHERE EXISTS (SELECT 1
FROM groups_people ps
WHERE p.id = ps.person_id and group_id = 1)
ORDER BY join_date DESC
LIMIT 10;
create table Person(
SSN INT,
Name VARCHAR(20),
primary key(SSN)
);
create table Car(
PlateNr INT,
Model VARCHAR(20),
primary key(PlateNr)
);
create table CarOwner(
SSN INT,
PlateNr INT,
primary key(SSN, PlateNR)
foreign key(SSN) references Person (SSN),
foreign key(PlateNr) references Car (PlateNr)
);
Insert into Person(SSN, Name) VALUES ('123456789','Max');
Insert into Person(SSN, Name) VALUES ('123456787','John');
Insert into Person(SSN, Name) VALUES ('123456788','Tom');
Insert into Car(PlateNr, Model) VALUES ('123ABC','Volvo');
Insert into Car(PlateNr, Model) VALUES ('321CBA','Toyota');
Insert into Car(PlateNr, Model) VALUES ('333AAA','Honda');
Insert into CarOwner(SSN, PlateNr) VALUES ('123456789','123ABC');
Insert into CarOwner(SSN, PlateNr) VALUES ('123456787','333AAA');
The problem I'm having is the SELECTE query I wanna make. I wan't to be able to SELECT everything from the Person and wan't the include the PlateNr of the car he's the owner of, an example:
PERSON
---------------------------------
SSN NAME Car
123456789 Max 123ABC
123456787 John 3338AAA
123456788 Tom
----------------------------------
So, I want to be able to show everything from the Person table and display the content of CarOwner aswell if the person is in fact a CarOwner. What I have so far is: "SELECT * from Person, CarOwner WHERE Person.SSN = CarOwner.SSN;". But this obviously results in only showing the person(s) that are CarOwners.
Hope I explained me well enough, Thanks.
Try this:
SELECT p.*, c.*
FROM Person p
LEFT OUTER JOIN CarOwner co
ON p.SSN = co.SSN
LEFT OUTER JOIN Car c
ON co.PlateNr = c.PlateNr
Show SQLFiddle
P.S. I've changed the type of your primary key PlateNr (in varchar and not in int)
select ssn, name, car
from Person p
LEFT OUTER JOIN CarOwner co
ON p.SSN = co.SSN
LEFT OUTER JOIN Car c
ON co.PlateNr = c.PlateNr