Indexing PostgreSQL JSONB Array Elements - postgresql

Question

Like the title says, how can I index a JSONB array?
The contents look like...
["some_value", "another_value"]
I can easily access the elements like...
SELECT * FROM table WHERE data->>0 = 'some_value';
I created an index like so...
CREATE INDEX table_data_idx ON table USING gin ((data) jsonb_path_ops);
When I run EXPLAIN, I still see it sequentially scanning...
What am I missing on indexing an array of text elements?

Answer 1

If you want to support that exact query with an index, the index would have to look like this:
CREATE INDEX ON "table" ((data->>0));
If you want to use the index you have, you cannot limit the search to just a specific array element (in your case, the first). You can speed up a search for some_value anywhere in the array:
SELECT * FROM "table"
WHERE data #> '["some_value"]'::jsonb;

Answer 2

I ended up taking a different approach. I am still having problems getting the search to work using a JSONB Type, so I ended up switching my column to a varchar ARRAY
CREATE TABLE table (
data varchar ARRAY NOT NULL
);
CREATE INDEX table_data_idx ON table USING GIN (data);
SELECT * FROM table WHERE data #> '{some_value}';
This works and is using the index.
I think my problem with my JSONB approach is because the element is actually nested much further and being treated as text.
i.e. data->'some_key'->>'array_key'->>0
And everytime I try to search I get all sorts of invalid token errors and other such things.

Answer 3

You may want to create a materialized view that has the primary key (or other unique index of your table) and expands the array field into a text column with the jsonb_array_elements_text function:
CREATE MATERIALIZED VIEW table_mv
AS
SELECT DISTINCT table.id, jsonb_array_elements_text(data->0) AS array_elem FROM table;
You can then create a unique index on this materialized view (primary keys are not supported on materialized views):
CREATE UNIQUE INDEX table_array_idx ON table_mv(id, array_elem);
Then query with a join to the original table on its primary key:
SELECT * FROM table INNER JOIN table_mv ON table.id = table_mv.id WHERE table_mv.array_elem = 'some_value';
This query should use the unique index and then look up the primary key of the original table, both very fast.