Bizarre behavior triggered by `SHOW TABLES FROM schema`

[beachhouse-spec]

What happens?

When executing SHOW TABLES FROM iceberg_catalog.demo and demo is a non-existent schema, duckdb_iceberg does not throw an error. Instead, it creates a local schema with the same name purely on the client side without issuing a REST request to create it on the catalog server.

I found that this issue is caused by a combination of duckdb_iceberg optimistically creating unknown schemas, and the special execution logic of SHOW TABLES FROM (which will not enter IcebergSchemaEntry::LookupEntry but IcebergSchemaEntry::Scan preventing the unknown schema entry's exists=false state from being reset).

I'd like to know if this behavior is by design or if it's considered a bug. If it's a bug, I'd be happy to submit a fix for it.

To Reproduce

attch 'iceberg_catalog' as iceberg_catalog (...);
SELECT schema_name FROM information_schema.schemata WHERE catalog_name ='iceberg_catalog';
┌─────────────┐
│ schema_name │
│   varchar   │
├─────────────┤
│ main        │
└─────────────┘
 show tables from demo;
┌─────────┐
│  name   │
│ varchar │
└─────────┘
  0 rows 
SELECT schema_name FROM information_schema.schemata WHERE catalog_name ='iceberg_catalog';
┌─────────────┐
│ schema_name │
│   varchar   │
├─────────────┤
│ demo        │
│ main        │
└─────────────┘

OS:

centos x86_64

DuckDB Version:

v1.6.0

DuckDB Client:

cli

Hardware:

No response

Full Name:

Jade Gong

Affiliation:

Tencent Corporation

Did you include all relevant data sets for reproducing the issue?

Yes

Did you include all code required to reproduce the issue?

• Yes, I have

Did you include all relevant configuration (e.g., CPU architecture, Python version, Linux distribution) to reproduce the issue?

• Yes, I have