POSTGRES - Combine same columns with different text in one row - sql

Question

I have three tables that i want to combine. I have a table doctor, patient and operation. Doctor represents all cind of doctors. Patient represents a patient and operation holds primaryKeys from patient and doctor.
How do i write a query which will show me chiefDoctor and assistantDocotor and Patient? What did i reach so far?
Show firstname and lastname from one either Chiefdoctor or Assistantdoctor. How do i write to show a table with both Chief and Assistant in it?
select a.vorname|| ' ' || a.nachname AS leitenderArzt, p.firstname || ' ' || p.lastname AS patient
from angestellter a inner join operation o on a.id = o.leitenderarzt
inner join patient p on o.patientident=p.ident
| id | firstname | lastname | patient |
| 1 | ImA | ChiefDoctor1 | p.firstname |
| 3 | ImA | ChiefDoctor3 | p.firstname |
The underlying structure of my database with a representation.
CREATE TABLE doctor
(
id serial NOT NULL,
firstname character varying(255) NOT NULL,
lastname character varying(255) NOT NULL,
CONSTRAINT angestellter_pkey PRIMARY KEY (id),
}
Table doctor
|id | firstname | lastname |
| 1 | ImA | ChiefDoctor1 |
| 2 | ImA | AssistantDoctor |
| 3 | ImA | ChiefDoctor2 |
CREATE TABLE patient
(
ident serial NOT NULL,
firstname character varying(255) NOT NULL,
lastname character varying(255) NOT NULL,
CONSTRAINT patient_pkey PRIMARY KEY (ident),
}
Table patient
| ident | firstname | lastname |
| 1 | Operated | ME |
CREATE TABLE operation
(
id serial NOT NULL,
chiefDoctor integer NOT NULL,
AssistantDoctor integer NOT NULL,
patientident integer NOT NULL,
CONSTRAINT operation_pkey PRIMARY KEY (id),
CONSTRAINT fkoperation539608 FOREIGN KEY (patientident)
REFERENCES patient (ident) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT fkoperation745809 FOREIGN KEY (assistantDoctor)
REFERENCES angestellter (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT fkoperation949671 FOREIGN KEY (chiefDoctor)
REFERENCES angestellter (id) MATCH SIMPLE
}
Table operation
| id | doctorID | doctorID | patientID |
| 1 | 1 | 2 | 1 |
How do i write a query which will show show who operated a patient with full name? It should look like this.
| id | chiefdoctor | assistantdoctor | patient |
|----| ImA + ChiefDoctor |ImA + AssistantDoctor | Operated + ME|

Answer 1

The first and perhaps most intuitive way of doing this is to join doctor twice:
select o.id
, d1.firstname || ' + ' || d1.lastname as chiefdoctor
, d2.firstname || ' + ' || d2.lastname as assistantdoctor
, p.firstname || ' + ' || p.lastname as patient
from operation o
join doctor d1
on o.chiefDoctor = d1.id
join doctor d2
on o.AssistantDoctor = d2.id
join patient p
on o.patientident = p.ident
You probably would like to trim names as in:
trim(both from d1.firstname) || ' + ' || trim(both from d1.lastname)
but I got the feeling that this was not the major concern you had so inorder to keep the solution shorter, I left that out