PostgreSQL query on text array value - sql

Question

I have a table where one column has an array - but stored in a text format:
mytable
id ids
-- -------
1 '[3,4]'
2 '[3,5]'
3 '[3]'
etc ...
I want to find all records that have the value 5 as an array element in the ids column.
I was trying to achieve this by using the "string to array" function and removing the [ symbols with the translate function, but couldn't find a way.

Answer 1

You can do this: http://www.sqlfiddle.com/#!1/5c148/12
select *
from tbl
where translate(ids, '[]','{}')::int[] && array[5];
Output:
| ID | IDS |
--------------
| 2 | [3,5] |
You can also use bool_or: http://www.sqlfiddle.com/#!1/5c148/11
with a as
(
select id, unnest(translate(ids, '[]','{}')::int[]) as elem
from tbl
)
select id
from a
group by id
having bool_or(elem = 5);
To see the original elements:
with a as
(
select id, unnest(translate(ids, '[]','{}')::int[]) as elem
from tbl
)
select id, '[' || array_to_string(array_agg(elem), ',') || ']' as ids
from a
group by id
having bool_or(elem = 5);
Output:
| ID | IDS |
--------------
| 2 | [3,5] |
Postgresql DDL is atomic, if it's not late yet in your project, just structure your stringly-typed array to a real array: http://www.sqlfiddle.com/#!1/6e18c/2
alter table tbl
add column id_array int[];
update tbl set id_array = translate(ids,'[]','{}')::int[];
alter table tbl drop column ids;
Query:
select *
from tbl
where id_array && array[5]
Output:
| ID | ID_ARRAY |
-----------------
| 2 | 3,5 |
You can also use contains operator: http://www.sqlfiddle.com/#!1/6e18c/6
select *
from tbl
where id_array #> array[5];
I prefer the && syntax though, it directly connotes intersection. It reflects that you are detecting if there's an intersection between two sets(array is a set)
http://www.postgresql.org/docs/8.2/static/functions-array.html

Answer 2

If you store the string representation of your arrays slightly differently, you can cast to array of integer directly:
INSERT INTO mytable
VALUES
(1, '{3,4}')
,(2, '{3,5}')
,(3, '{3}');
SELECT id, ids::int[]
FROM mytable;
Else, you have to put in one more step:
SELECT (translate(ids, '[]','{}'))::int[]
FROM mytable
I would consider making the column an array type to begin with.
Either way, you can find your row like this:
SELECT id, ids
FROM (
SELECT id, ids, unnest(ids::int[]) AS elem
FROM mytable
) x
WHERE elem = 5