Re: filter records by substring match of an postgresql array column

I enabled the extension `pg_trgm`.

I thought to query like:

SELECT
"videos".*
FROM
"videos"
WHERE
(
array_to_string(tags, ', ') ilike '%web shorts%'
)
AND EXISTS
(
SELECT
FROM
unnest(tags) AS u(val)
WHERE
u.val ILIKE '%web shorts%'
)
;

And to do I wanted to add an index like:

CREATE INDEX trgm_idx_video_tags ON videos USING gist ((array_to_string(tags, ', ')) gist_trgm_ops)

But on running this I get an error as:

ERROR: functions in index expression must be marked IMMUTABLE

How can I fix this?

> On Nov 8, 2017, at 4:02 PM, Arup Rakshit <aruprakshit1987(at)outlook(dot)com> wrote:
>
> Hi,
>
> I do have a videos table, and it has a column called `tags` of type array. I would like to select all videos where any string inside tag column matches a given substring. What method should I use? The *Contains `@>` operator* will do full string comparisons as far as I understood.