terrymanu commented on issue #22553:
URL:
https://github.com/apache/shardingsphere/issues/22553#issuecomment-3635553517
## Understanding
- Environment: ShardingSphere-Proxy 5.2.2-SNAPSHOT (commit 753c0cee…),
Cluster mode, two data sources ds_0/ds_1 (even/odd sharding),
sql-federation-type=ADVANCED.
- Symptom: View select_view on t_order returns only even user_id
(10,12…28); direct query select distinct(user_id) from t_order order by user_id
returns full 10–29 set.
## Root Cause
- The view is not defined in sharding rules; create view runs only on the
default data source ds_0, and select * from select_view is routed only to ds_0.
The view reads ds_0’s physical t_order, so results include only that shard’s
data.
- Advanced Federation does not expand cross-shard views or auto-broadcast
DDL; there is also no metadata lock/consistency, so concurrent DDL or
multi-instance deployments can leave the view present on some nodes only.
## Analysis
- Logs show Actual SQL for create view and select * from select_view only
on ds_0, while the distinct query on the sharded table hits ds_0+ds_1, matching
the “even-only” result.
- ShardingSphere usage convention: objects not declared in rules default
to single-database routing; cross-shard logical views are not automatically
aggregated. Running DDL immediately and without metadata locking means
multi-instance/multi-connection DDL can diverge
the view state across nodes.
## Conclusion
- This is a usage limitation, not a confirmed product bug. Avoid creating
cross-shard views through Proxy on sharded tables. Use the raw SQL (select
distinct(user_id) from t_order order by user_id) directly, or, if you insist on
a view, manually create identical views
on every shard and access them explicitly (routing still defaults to a
single db). If you must run DDL, keep it single-instance and serialized to
avoid metadata races. If the issue persists, please share whether multiple
Proxy instances/clients ran DDL concurrently,
per-shard existence of the view, and full routing/log details.
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