Fetch results of joined tables as columns in postgres - sql

Question

I trying to figure out a way to generate a SQL query, to be used in a view, to generate an Excel like format for parent-child relationship.
I have the following tables
Person
id
name
email
accepted
1
A
--
--
2
B
--
--
3
C
--
--
Guest
id
name
accepted
id_person (foreign_key -> person.id)
1
AGuest1
---
1
2
BGuest1
---
2
3
BGuest2
---
2
4
CGuest1
---
3
5
CGuest2
---
3
6
CGuest3
---
3
A person can have multiple guests accompanying him/her.
What I want to do is generate a SQL that gives me the following result:
Person Name
Guest 1 Name
Guest 2 Name
Guest 3 Name
A
AGuest1
--
--
B
BGuest1
BGuest2
--
C
CGuest1
CGuest2
CGuest3
I can generate two separate queries that will generate a list of rows with that information but I am struggling to generate multiple columns based on the information that I have.
I have looked into crosstab() for postgres, but so far I have no luck with generating anything that would like this.
Any help or pointers in the right direction would be helpful, thank you!

Answer 1

You can use CROSSTAB:
SELECT *
FROM CROSSTAB (
'SELECT p.name, g.name, g.name
FROM person p JOIN guest g
ON p.id = g.id_person
ORDER BY 1,2')
AS ("Person Name" varchar(100), "Guest 1 Name" varchar(100),
"Guest 2 Name" varchar(100), "Guest 3 Name" varchar(100));
Please note: This will work for 1 to 3 guest like you described. In case more guests per person are possible, you need to extend this.
I created a working example here: db<>fiddle