Clickhouse datasource plugin returns error in Grafana explore page when query with a LowCardinality(Nullable(String)) column

[linjunzhe]

What happened:
It returned an error if a table contains a LowCardinality(Nullable(String)) column.

sql: Scan error on column index 0, name "src_tor_name": unsupported Scan, storing driver.Value type *string into type *string: Could not process SQL results

What you expected to happen:
It should return the data same as clickhouse-client.

How to reproduce it (as minimally and precisely as possible):

1. Create a table with a LowCardinality(Nullable(String)) column, for example

CREATE TABLE pingmesh.test ON CLUSTER staging
(
    `src_tor_name` LowCardinality(Nullable(String)),
    `loss_count` Int64,
    `unixtime` DateTime('Etc/UTC') CODEC(DoubleDelta)
)
ENGINE = ReplicatedMergeTree('/clickhouse/{installation}/{cluster}/tables/{shard}/pingmesh/test', '{replica}')
PARTITION BY toYYYYMMDD(unixtime)
PRIMARY KEY unixtime
ORDER BY unixtime
SETTINGS index_granularity = 8192

2. Insert some data

INSERT INTO pingmesh.test (*) VALUES ('test', 0, 0)

3. Query the data from clickhouse client. It works fine.

> SELECT * FROM "pingmesh"."test" LIMIT 10
SELECT *
FROM pingmesh.test
LIMIT 10

Query id: fd6dea33-12b2-4ae2-aaa4-c2e8601742cf

┌─src_tor_name─┬─loss_count─┬────────────unixtime─┐
│ test         │          0 │ 1970-01-01 00:00:00 │
└──────────────┴────────────┴─────────────────────┘

1 row in set. Elapsed: 0.001 sec.

4. Put the same query in Grafana Explore with Clickhouse datasource.
   

Screenshots

Anything else we need to know?:

1. I was upgrade Grafana recently to the newest 10.4.3. The previous version I used is 10.2.3, which was working fine.
2. I tested with Nullable(String) or LowCardinality(String) DEFAULT '' columns, the plugin works as expected.

Environment:

• Grafana version: 10.4.3
• Plugin version: 4.0.7
• OS Grafana is installed on: Grafana official docker image
• User OS & Browser: macOS 13.5.2, Chrome
• Others:

[linjunzhe]

Hi, could anyone help?

[SpencerTorres]

Apologies, I thought this was resolved in #805 + #814

If it's still an issue I can try reproducing the error and seeing why the fix isn't working in this case.

At the cost of losing some newer patches, you can downgrade to v4.0.4 and this should be fixed. The change that was made in v4.0.5 may have caused this regression.

[SpencerTorres]

Should be fixed and released in the related PR. Let me know if you're still having issues after updating. Thanks!