Convert comma separated id to comma separated string in postgresql - postgresql

Question

I have comma separated column which represents the ids of emergency type like:
ID | Name
1 | 1,2,3
2 | 1,2
3 | 1
I want to make query to get name of the this value field.
1 - Ambulance
2 - Fire
3 - Police
EXPECTED OUTPUT
1 - Ambulance, Fire, Police
2 - Ambulance, Fire
3 - Ambulance
I just need to write select statement in postgresql to display string values instead of integer values in comma separated.

Answer 1

Comma separated values is bad database design practice, though postgre is so feature rich, that you can handle this task easily.
-- just simulate tables
with t1(ID, Name) as(
select 1 ,'1,2,3' union all
select 2 ,'1,2' union all
select 3 ,'1'
),
t2(id, name) as(
select 1, 'Ambulance' union all
select 2, 'Fire' union all
select 3, 'Police'
)
-- here is actual query
select s1.id, string_agg(t2.name, ',') from
( select id, unnest(string_to_array(Name, ','))::INT as name_id from t1 ) s1
join t2
on s1.name_id = t2.id
group by s1.id
demo
Though, if you can, change your approach. Right database design means easy queries and better performance.

Answer 2

To get the values for each of the ids is a simple query: select * from ;. Once you have the values you will have to parse the strings with a delimiter of ','. then you would have to assign the parsed sting values to the appropriate job titles, and remake the list. Are you writing this in a specific language?
or you could just assign the sorted value to something like 1,2,3 is equal to "some string", 1,2 is equal to "some other string", etc.

Answer 3

Assuming you have a table with the ids and values for Ambulance, Police and Fire, then you can use something like the following.
CREATE TABLE public.test1
(
id integer NOT NULL,
commastring character varying,
CONSTRAINT pk_test1 PRIMARY KEY (id)
);
INSERT INTO public.test1
VALUES (1, '1,2,3'), (2, '1,2'), (3, '1');
CREATE TABLE public.test2
(
id integer NOT NULL,
description character varying,
CONSTRAINT pk_test2 PRIMARY KEY (id)
);
INSERT INTO public.test2
VALUES (1, 'Ambulance'), (2, 'Fire'), (3, 'Police');
with descs as
(with splits as
(SELECT id, split_part(commastring, ',', 1) as col2,
split_part(commastring, ',', 2) as col3, split_part(commastring, ',', 3) as col4 from test1)
select splits.id, t21.description as d1, t22.description as d2, t23.description as d3
from splits
inner join test2 t21 on t21.id::character varying = splits.col2
left join test2 t22 on t22.id::character varying = splits.col3
left join test2 t23 on t23.id::character varying = splits.col4)
SELECT descs.id, CASE WHEN d2 IS NOT NULL AND d3 IS NOT NULL
THEN CONCAT_WS(',', d1,d2,d3) ELSE CASE WHEN d2 IS NOT NULL
THEN CONCAT_WS(',', d1,d2) ELSE d1 END END FROM descs
ORDER BY id;
By way of explanation, I give the create table and insert commands, so that you (and others) can follow the logic. It would help enormously, if you were to do this in your questions, as it saves everyone time and avoids misunderstandings.
My inner CTE then splits the string using split_part. The syntax here is quite simple, field, separator and desired column within the field to be split (so in this case we need one, two and three). I then join the split columns to test2. Note two things here: the first join is an inner join, as there will always be at least one column in the split (I am assuming!!!), whereas the other two are left joins; secondly, the split of a character varying field in turn produces character varying splits, so I have to cast the int id to character varying for the join to work. Doing the cast this way round (i.e. id to character varying rather than character varying to id) means I don't have to bother about nulls. Finally depending on the number of nulls present, I concatenate the results with the given separator. Again I am assuming d1 will always have a value.
HTH