fix: Alter destination table along with mv on schema changes

[pkotikalapudi]

Summary

Alter destination table along with materialized views on update.

Currently when we update a model materialized='materialized_view' it only updates underlying materialized view but not the destination table it is attached to. This issue is also brought up before.

This PR provides the ability to update the destination table along with Materialized view. It uses on_schema_change

Checklist

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[CLAassistant]

Corporate CLA signed.

[windsurf-bot]

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[windsurf-bot]

The code should check if existing_relation exists before attempting to apply schema changes. Without this check, the code might try to apply schema changes to a non-existent relation.

Suggested change

	{%- set on_schema_change = incremental_validate_on_schema_change(config.get('on_schema_change'), default='ignore') -%}
	{{ log('on_schema_change strategy for destination table of MV: ' + on_schema_change, info=True) }}
	{%- if on_schema_change != 'ignore' -%}
	{%- set column_changes = adapter.check_incremental_schema_changes(on_schema_change, existing_relation, sql) -%}
	{% if column_changes %}
	{% do clickhouse__apply_column_changes(column_changes, existing_relation) %}
	{% set existing_relation = load_cached_relation(this) %}
	{% endif %}
	{%- endif %}
	{%- set on_schema_change = incremental_validate_on_schema_change(config.get('on_schema_change'), default='ignore') -%}
	{{ log('on_schema_change strategy for destination table of MV: ' + on_schema_change, info=True) }}
	{%- if existing_relation is not none and on_schema_change != 'ignore' -%}
	{%- set column_changes = adapter.check_incremental_schema_changes(on_schema_change, existing_relation, sql) -%}
	{% if column_changes %}
	{% do clickhouse__apply_column_changes(column_changes, existing_relation) %}
	{% set existing_relation = load_cached_relation(this) %}
	{% endif %}
	{%- endif %}

[pkotikalapudi]

The default behavior in case of on_schema_change non existent is to ignore destination table change and just update the MV (current implementation)

[pkotikalapudi]

@koletzilla Please take a look at this while I add/update tests for multiple MV and RMV

[pkotikalapudi]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.You have signed the CLA already but the status is still pending? Let us recheck it.

CCLA has been signed by Twilio. Is there somebody who can validate it?

[alexey-milovidov]

I validated, all ok.