LIKE query on elements of flat jsonb array

Question

I have a Postgres table posts with a column of type jsonb which is basically a flat array of tags.

What i need to do is to somehow run a LI

Answer 1

SELECT *
FROM   posts p
WHERE  EXISTS (
   SELECT FROM jsonb_array_elements_text(p.tags) tag
   WHERE  tag LIKE '%TAG%'
   );

Related, with explanation:

• Search a JSON array for an object containing a value matching a pattern

Or simpler with the @? operator since Postgres 12 implemented SQL/JSON:

SELECT *
--     optional to show the matching item:
--   , jsonb_path_query_first(tags, '$[*] ? (@ like_regex "^ tag" flag "i")')
FROM   posts
WHERE  tags @? '$[*] ? (@ like_regex "TAG")';

The operator @? is just a wrapper around the function jsonb_path_exists(). So this is equivalent:

...
WHERE  jsonb_path_exists(tags, '$[*] ? (@ like_regex "TAG")');

Neither has index support. (May be added for the @? operator later, but not there in pg 13, yet). So those queries are slow for big tables. A normalized design, like Laurenz already suggested would be superior - with a trigram index:

• PostgreSQL LIKE query performance variations

For just prefix matching (LIKE 'TAG%', no leading wildcard), you could make it work with a full text index:

CREATE INDEX posts_tags_fts_gin_idx ON posts USING GIN (to_tsvector('simple', tags));

And a matching query:

SELECT *
FROM   posts p
WHERE  to_tsvector('simple', tags)  @@ 'TAG:*'::tsquery

Or use the english dictionary instead of simple (or whatever fits your case) if you want stemming for natural English language.

to_tsvector(json(b)) requires Postgres 10 or later.

Related:

• Get partial match from GIN indexed TSVECTOR column
• Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL