how to get rows value in one row?

Question

Select id
from x

gives a list of ids:

1
2
3
44
655
31

how Do i get it in one row as array? like (1,2,3,44,655,31)

Answer 1

SQLFiddle Demo

SELECT 
array_to_string(array_agg(id),',') as agg_id 
from x

Answer 2

Query should be like this

 SELECT string_agg(id, ',') FROM x