feat: database level default connection configuration

[dantengsky]

I hereby agree to the terms of the CLA available at: https://docs.databend.com/dev/policies/cla/

Summary

Two New Database-Level Options

DEFAULT_STORAGE_CONNECTION, DEFAULT_STORAGE_PATH

These options define the default storage connection and path for the database. Any table created in the database without explicit storage settings will inherit these database-level defaults.

You can set the options when creating the database, or adjust them later with ALTER DATABASE.

Example

CREATE CONNECTION IF NOT EXISTS prod_s3
  STORAGE_TYPE = 's3'
  ACCESS_KEY_ID = '***'
  SECRET_ACCESS_KEY = '***';

CREATE DATABASE analytics OPTIONS (
  DEFAULT_STORAGE_CONNECTION = 'prod_s3',
  DEFAULT_STORAGE_PATH = 's3://mybucket/analytics/'
);

SHOW CREATE DATABASE analytics;

+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------+
| Database  | Create Database                                                                                                                                   |
+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------+
| analytics | CREATE DATABASE `analytics` ENGINE=DEFAULT OPTIONS (DEFAULT_STORAGE_CONNECTION='prod_s3', DEFAULT_STORAGE_PATH='s3://mybucket/analytics/') |
+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------+

USE analytics;

CREATE TABLE t AS SELECT 1;

SELECT storage_param
FROM system.tables
WHERE database = 'analytics' AND name = 't';

+-------------------------------------------------------------------------------------------------------+
| storage_param                                                                                         |
+-------------------------------------------------------------------------------------------------------+
| s3 | bucket=mybucket,root=/analytics/,endpoint=https://s3.amazonaws.com,ak=******,iam_role=           |
+-------------------------------------------------------------------------------------------------------+

ALTER DATABASE analytics SET OPTIONS (
  DEFAULT_STORAGE_PATH = 's3://mybucket/analytics_v2/'
);

CREATE TABLE t_v2 AS SELECT 1;

SELECT storage_param
FROM system.tables
WHERE database = 'analytics' AND name = 't_v2';

+----------------------------------------------------------------------------------------------------------+
| storage_param                                                                                            |
+----------------------------------------------------------------------------------------------------------+
| s3 | bucket=mybucket,root=/analytics_v2/,endpoint=https://s3.amazonaws.com,ak=******,iam_role=           |
+----------------------------------------------------------------------------------------------------------+

Notes:

• When creating a database you cannot supply only one of DEFAULT_STORAGE_CONNECTION or DEFAULT_STORAGE_PATH; they must appear together or both be omitted.

• When altering an existing database you may change one option at a time as long as the other option already exists; otherwise the command fails.

• During CREATE DATABASE/ALTER DATABASE, connection reachability and storage path permissions are validated.

• Updating these database-level options does not change storage parameters of existing tables; only tables created afterwards use the new defaults.

• fixes: Feature Request: Database level default connection configuration #18825

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

---

This change is 

[dantengsky]

@codex review

[dantengsky]

@codex review

[chatgpt-codex-connector]

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