From 26eb7726da05ec54bcf6726a65d60c56bd3efe66 Mon Sep 17 00:00:00 2001
From: the4thamigo-uk <7022874+the4thamigo-uk@users.noreply.github.com>
Date: Thu, 21 Nov 2024 12:18:06 +0000
Subject: [PATCH] Prevent data loss when updating materialized view (#383)

---
 CHANGELOG.md                                  |  5 ++
 .../materializations/materialized_view.sql    | 67 +++++++++++++------
 2 files changed, 53 insertions(+), 19 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0e23f02c..c0f584c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+### Unreleased
+
+### Improvement
+* Materialized view now attempts to use `ALTER TABLE...MODIFY QUERY` to update existing materialized views. This is an atomic operation so data is not lost. ([#390](https://github.com/ClickHouse/dbt-clickhouse/pull/390))
+
 ### Release [1.8.5], 2024-11-19
 
 ### New Features
diff --git a/dbt/include/clickhouse/macros/materializations/materialized_view.sql b/dbt/include/clickhouse/macros/materializations/materialized_view.sql
index 4583918b..e219ec0e 100644
--- a/dbt/include/clickhouse/macros/materializations/materialized_view.sql
+++ b/dbt/include/clickhouse/macros/materializations/materialized_view.sql
@@ -84,19 +84,25 @@
     {% else %}
         {{ log('No existing mvs found matching the pattern. continuing..', info=True) }}
     {% endif %}
-    {{ clickhouse__drop_mvs(target_relation, cluster_clause, views) }}
     {% if should_full_refresh() %}
+      {{ clickhouse__drop_mvs(target_relation, cluster_clause, views) }}
+
       {% call statement('main') -%}
         {{ get_create_table_as_sql(False, backup_relation, sql) }}
       {%- endcall %}
       {% do exchange_tables_atomic(backup_relation, existing_relation) %}
+
+      {{ clickhouse__create_mvs(existing_relation, cluster_clause, views) }}
     {% else %}
       -- we need to have a 'main' statement
       {% call statement('main') -%}
         select 1
       {%- endcall %}
+
+      -- try to alter view first to replace sql, else drop and create
+      {{ clickhouse__update_mvs(target_relation, cluster_clause, views) }}
+
     {% endif %}
-    {{ clickhouse__create_mvs(existing_relation, cluster_clause, views) }}
   {% else %}
     {{ log('Replacing existing materialized view ' + target_relation.name) }}
     {{ clickhouse__replace_mv(target_relation, existing_relation, intermediate_relation, backup_relation, sql, views) }}
@@ -142,31 +148,54 @@
 {%- endmacro %}
 
 {% macro clickhouse__drop_mv(mv_relation, cluster_clause)  -%}
+  {% call statement('drop existing mv: ' + mv_relation.name) -%}
     drop view if exists {{ mv_relation }} {{ cluster_clause }}
-{%- endmacro %}u
+  {% endcall %}
+{%- endmacro %}
 
-{% macro clickhouse__create_mv(mv_relation, target_table, cluster_clause, sql)  -%}
-  create materialized view if not exists {{ mv_relation }} {{ cluster_clause }}
-  to {{ target_table }}
-  as {{ sql }}
+{% macro clickhouse__create_mv(mv_relation, target_relation, cluster_clause, view_sql)  -%}
+  {% call statement('create existing mv: ' + mv_relation.name) -%}
+    create materialized view if not exists {{ mv_relation }} {{ cluster_clause }}
+    to {{ target_relation }}
+    as {{ view_sql }}
+  {% endcall %}
+{%- endmacro %}
+
+{% macro clickhouse__modify_mv(mv_relation, cluster_clause, view_sql)  -%}
+  {% call statement('modify existing mv: ' + mv_relation.name) -%}
+    alter table {{ mv_relation }} {{ cluster_clause }} modify query {{ view_sql }}
+  {% endcall %}
+{%- endmacro %}
+
+{% macro clickhouse__update_mv(mv_relation, target_relation, cluster_clause, view_sql)  -%}
+  {% set existing_relation = adapter.get_relation(database=mv_relation.database, schema=mv_relation.schema, identifier=mv_relation.identifier) %}
+  {% if existing_relation %}
+    {{ clickhouse__modify_mv(mv_relation, cluster_clause, view_sql) }};
+  {% else %}
+    {{ clickhouse__drop_mv(mv_relation, cluster_clause) }};
+    {{ clickhouse__create_mv(mv_relation, target_relation, cluster_clause, view_sql) }};
+  {% endif %}
 {%- endmacro %}
 
 {% macro clickhouse__drop_mvs(target_relation, cluster_clause, views)  -%}
-    {% for view in views.keys() %}
-      {%- set mv_relation = target_relation.derivative('_' + view, 'materialized_view') -%}
-      {% call statement('drop existing mv: ' + view) -%}
-        {{ clickhouse__drop_mv(mv_relation, cluster_clause) }};
-      {% endcall %}
-    {% endfor %}
+  {% for view in views.keys() %}
+    {%- set mv_relation = target_relation.derivative('_' + view, 'materialized_view') -%}
+    {{ clickhouse__drop_mv(mv_relation, cluster_clause) }};
+  {% endfor %}
 {%- endmacro %}
 
 {% macro clickhouse__create_mvs(target_relation, cluster_clause, views)  -%}
-    {% for view, view_sql in views.items() %}
-      {%- set mv_relation = target_relation.derivative('_' + view, 'materialized_view') -%}
-      {% call statement('create existing mv: ' + view) -%}
-        {{ clickhouse__create_mv(mv_relation, target_relation, cluster_clause, view_sql) }};
-      {% endcall %}
-    {% endfor %}
+  {% for view, view_sql in views.items() %}
+    {%- set mv_relation = target_relation.derivative('_' + view, 'materialized_view') -%}
+    {{ clickhouse__create_mv(mv_relation, target_relation, cluster_clause, view_sql) }};
+  {% endfor %}
+{%- endmacro %}
+
+{% macro clickhouse__update_mvs(target_relation, cluster_clause, views)  -%}
+  {% for view, view_sql in views.items() %}
+    {%- set mv_relation = target_relation.derivative('_' + view, 'materialized_view') -%}
+    {{ clickhouse__update_mv(mv_relation, target_relation, cluster_clause, view_sql) }};
+  {% endfor %}
 {%- endmacro %}
 
 {% macro clickhouse__replace_mv(target_relation, existing_relation, intermediate_relation, backup_relation, sql, views) %}