mysql protocol does not support error during query execution

[superceix]

Describe the bug
sql cannot read error msg by mysql client if table is on cluster

Does it reproduce on recent release?
server: clickhouse 21.2.4.6
client: mysql client 8.0.20、msyql client 5.7.26 access through mysql_port

How to reproduce

• create table on cluster

CREATE TABLE `test`.`t7_all` ON CLUSTER cluster_1 (`id` Int64, `createtime` Date)  ENGINE = ReplicatedMergeTree('/clickhouse/cluster1/{layer}-{shard}/t7', '{replica}')  PARTITION BY createtime ORDER BY id SETTINGS index_granularity=8192;

• create table names test.t7_all again

CREATE TABLE `test`.`t7_all` ON CLUSTER cluster_1 (`id` Int64, `createtime` Date)  ENGINE = ReplicatedMergeTree('/clickhouse/cluster1/{layer}-{shard}/t7', '{replica}')  PARTITION BY createtime ORDER BY id SETTINGS index_granularity=8192;

Expected behavior
mysql client get error message same with clickhouse client: Table test.t7_all already exists

Error message and/or stacktrace
mysql client cannot read err message and report:

Lost connection to MySQL server during query

Additional context
Add any other context about the problem here.

[tavplubix]

It's because ON CLUSTER queries return table with query execution status. Seems like mysql client does not expect that DDL query may return some data.

[superceix]

It's because ON CLUSTER queries return table with query execution status. Seems like mysql client does not expect that DDL query may return some data.

Will you support this in the future?

[tavplubix]

The reason is that ClickHouse sends ERR_Packet with incorrect sequence number, so MySQL client does not recognize it as a part of COM_QUERY_Response and resets connection. It happens if exception is thrown during query execution:

mysql> select throwIf(number) from numbers(2) settings max_block_size=1;
ERROR 2013 (HY000): Lost connection to MySQL server during query

I will try to fix it