24.8.14 Backport of #75622: Allow altering database comment

docs/en/sql-reference/statements/alter/database-comment.md

@@ -0,0 +1,55 @@
+---
+description: 'Documentation for ALTER DATABASE ... MODIFY COMMENT Statements'
+slug: /sql-reference/statements/alter/database-comment
+sidebar_position: 51
+sidebar_label: 'UPDATE'
+title: 'ALTER DATABASE ... MODIFY COMMENT Statements'
+---
+
+# ALTER DATABASE ... MODIFY COMMENT
+
+Adds, modifies, or removes comment to the table, regardless if it was set before or not. Comment change is reflected in both [system.databases](/operations/system-tables/databases.md) and `SHOW CREATE DATABASE` query.
+
+**Syntax**
+
+``` sql
+ALTER DATABASE [db].name [ON CLUSTER cluster] MODIFY COMMENT 'Comment'
+```
+
+**Examples**
+
+Creating a DATABASE with comment (for more information, see the [COMMENT](/sql-reference/statements/create/table#comment-clause) clause):
+
+``` sql
+CREATE DATABASE database_with_comment ENGINE = Memory COMMENT 'The temporary database';
+```
+
+Modifying the table comment:
+
+``` sql
+ALTER DATABASE database_with_comment MODIFY COMMENT 'new comment on a database';
+SELECT comment FROM system.databases WHERE name = 'database_with_comment';
+```
+
+Output of a new comment:
+
+```text
+┌─comment─────────────────┐
+│ new comment on database │
+└─────────────────────────┘
+```
+
+Removing the database comment:
+
+``` sql
+ALTER DATABASE database_with_comment MODIFY COMMENT '';
+SELECT comment FROM system.databases WHERE  name = 'database_with_comment';
+```
+
+Output of a removed comment:
+
+```text
+┌─comment─┐
+│         │
+└─────────┘
+```

src/Access/Common/AccessType.h

@@ -42,6 +42,7 @@ enum class AccessType : uint8_t
     M(ALTER_MATERIALIZE_COLUMN, "MATERIALIZE COLUMN", COLUMN, ALTER_COLUMN) \
     M(ALTER_COLUMN, "", GROUP, ALTER_TABLE) /* allow to execute ALTER {ADD|DROP|MODIFY...} COLUMN */\
     M(ALTER_MODIFY_COMMENT, "MODIFY COMMENT", TABLE, ALTER_TABLE) /* modify table comment */\
+    M(ALTER_MODIFY_DATABASE_COMMENT, "MODIFY DATABASE COMMENT", DATABASE, ALTER_DATABASE) /* modify database comment*/\
     \
     M(ALTER_ORDER_BY, "ALTER MODIFY ORDER BY, MODIFY ORDER BY", TABLE, ALTER_INDEX) \
     M(ALTER_SAMPLE_BY, "ALTER MODIFY SAMPLE BY, MODIFY SAMPLE BY", TABLE, ALTER_INDEX) \

src/Databases/DatabaseMemory.cpp

@@ -211,6 +211,11 @@ std::vector<std::pair<ASTPtr, StoragePtr>> DatabaseMemory::getTablesForBackup(co
     return res;
 }
 
+void DatabaseMemory::alterDatabaseComment(const AlterCommand & command)
+{
+    DB::updateDatabaseCommentWithMetadataFile(shared_from_this(), command);
+}
+
 void registerDatabaseMemory(DatabaseFactory & factory)
 {
     auto create_fn = [](const DatabaseFactory::Arguments & args)

src/Databases/DatabaseMemory.h

@@ -52,6 +52,8 @@ class DatabaseMemory final : public DatabaseWithOwnTablesBase
 
     std::vector<std::pair<ASTPtr, StoragePtr>> getTablesForBackup(const FilterByNameFunction & filter, const ContextPtr & local_context) const override;
 
+    void alterDatabaseComment(const AlterCommand & alter_command) override;
+
 private:
     void removeDataPath(ContextPtr local_context);
 

src/Databases/DatabaseOnDisk.cpp

@@ -19,6 +19,7 @@
 #include <Parsers/ParserCreateQuery.h>
 #include <Parsers/formatAST.h>
 #include <Parsers/parseQuery.h>
+#include <Storages/AlterCommands.h>
 #include <Storages/IStorage.h>
 #include <Storages/StorageFactory.h>
 #include <TableFunctions/TableFunctionFactory.h>
@@ -860,4 +861,11 @@ void DatabaseOnDisk::modifySettingsMetadata(const SettingsChanges & settings_cha
 
     fs::rename(metadata_file_tmp_path, metadata_file_path);
 }
+
+void DatabaseOnDisk::alterDatabaseComment(const AlterCommand & command)
+{
+    DB::updateDatabaseCommentWithMetadataFile(shared_from_this(), command);
+}
+
+
 }

src/Databases/DatabaseOnDisk.h

@@ -11,6 +11,8 @@ namespace DB
 {
 
 class Context;
+struct AlterCommand;
+
 std::pair<String, StoragePtr> createTableFromAST(
     ASTCreateQuery ast_create_query,
     const String & database_name,
@@ -76,6 +78,8 @@ class DatabaseOnDisk : public DatabaseWithOwnTablesBase
 
     void modifySettingsMetadata(const SettingsChanges & settings_changes, ContextPtr query_context);
 
+    void alterDatabaseComment(const AlterCommand & alter_command) override;
+
 protected:
     static constexpr const char * create_suffix = ".tmp";
     static constexpr const char * drop_suffix = ".tmp_drop";

src/Databases/DatabasesCommon.cpp

@@ -9,6 +9,10 @@
 #include <Parsers/ASTSelectWithUnionQuery.h>
 #include <Parsers/ParserCreateQuery.h>
 #include <Parsers/formatAST.h>
+#include <Parsers/parseQuery.h>
+#include <Storages/AlterCommands.h>
+#include <Storages/ColumnsDescription.h>
+#include <Storages/KeyDescription.h>
 #include <Storages/StorageDictionary.h>
 #include <Storages/StorageFactory.h>
 #include <Storages/Utils.h>
@@ -30,6 +34,7 @@ namespace ErrorCodes
     extern const int NOT_IMPLEMENTED;
     extern const int LOGICAL_ERROR;
     extern const int CANNOT_GET_CREATE_TABLE_QUERY;
+    extern const int BAD_ARGUMENTS;
 }
 
 void applyMetadataChangesToCreateQuery(const ASTPtr & query, const StorageInMemoryMetadata & metadata)
@@ -206,6 +211,24 @@ void cleanupObjectDefinitionFromTemporaryFlags(ASTCreateQuery & query)
     query.out_file = nullptr;
 }
 
+void updateDatabaseCommentWithMetadataFile(DatabasePtr db, const AlterCommand & command)
+{
+    if (!command.comment)
+        throw Exception(ErrorCodes::BAD_ARGUMENTS, "Unable to obtain database comment from query");
+
+    String old_database_comment = db->getDatabaseComment();
+    db->setDatabaseComment(command.comment.value());
+
+    try
+    {
+        DatabaseCatalog::instance().updateMetadataFile(db);
+    }
+    catch (...)
+    {
+        db->setDatabaseComment(old_database_comment);
+        throw;
+    }
+}
 
 DatabaseWithOwnTablesBase::DatabaseWithOwnTablesBase(const String & name_, const String & logger, ContextPtr context_)
         : IDatabase(name_), WithContext(context_->getGlobalContext()), log(getLogger(logger))

src/Databases/DatabasesCommon.h

@@ -21,6 +21,8 @@ void cleanupObjectDefinitionFromTemporaryFlags(ASTCreateQuery & query);
 
 class Context;
 
+void updateDatabaseCommentWithMetadataFile(DatabasePtr db, const AlterCommand & command);
+
 /// A base class for databases that manage their own list of tables.
 class DatabaseWithOwnTablesBase : public IDatabase, protected WithContext
 {

src/Databases/IDatabase.cpp

@@ -55,6 +55,11 @@ IDatabase::~IDatabase()
     CurrentMetrics::sub(CurrentMetrics::AttachedDatabase, 1);
 }
 
+void IDatabase::alterDatabaseComment(const AlterCommand & /*command*/)
+{
+    throw Exception(ErrorCodes::NOT_IMPLEMENTED, "{}: ALTER DATABASE COMMENT is not supported", getEngineName());
+}
+
 std::vector<std::pair<ASTPtr, StoragePtr>> IDatabase::getTablesForBackup(const FilterByNameFunction &, const ContextPtr &) const
 {
     /// Cannot backup any table because IDatabase doesn't own any tables.

src/Databases/IDatabase.h

@@ -25,12 +25,14 @@
 namespace DB
 {
 
+
 struct Settings;
 struct ConstraintsDescription;
 struct IndicesDescription;
 struct StorageInMemoryMetadata;
 struct StorageID;
 class ASTCreateQuery;
+struct AlterCommand;
 class AlterCommands;
 class SettingsChanges;
 using DictionariesWithID = std::vector<std::pair<String, UUID>>;
@@ -416,6 +418,10 @@ class IDatabase : public std::enable_shared_from_this<IDatabase>
         std::lock_guard lock{mutex};
         return database_name;
     }
+
+    // Alter comment of database.
+    virtual void alterDatabaseComment(const AlterCommand &);
+
     /// Get UUID of database.
     virtual UUID getUUID() const { return UUIDHelpers::Nil; }
 

src/Databases/MySQL/DatabaseMySQL.cpp

@@ -16,12 +16,20 @@
 #    include <QueryPipeline/QueryPipelineBuilder.h>
 #    include <IO/Operators.h>
 #    include <Interpreters/Context.h>
+#    include <Interpreters/DatabaseCatalog.h>
 #    include <Interpreters/evaluateConstantExpression.h>
 #    include <Parsers/ASTCreateQuery.h>
 #    include <Parsers/ASTFunction.h>
 #    include <Parsers/ParserCreateQuery.h>
 #    include <Parsers/parseQuery.h>
 #    include <Parsers/queryToString.h>
+#    include <Processors/Executors/PullingPipelineExecutor.h>
+#    include <Processors/Sources/MySQLSource.h>
+#    include <QueryPipeline/QueryPipelineBuilder.h>
+#    include <Storages/AlterCommands.h>
+#    include <Storages/MySQL/MySQLHelpers.h>
+#    include <Storages/MySQL/MySQLSettings.h>
+#    include <Storages/NamedCollectionsHelpers.h>
 #    include <Storages/StorageMySQL.h>
 #    include <Storages/MySQL/MySQLSettings.h>
 #    include <Storages/MySQL/MySQLHelpers.h>
@@ -411,6 +419,11 @@ StoragePtr DatabaseMySQL::detachTable(ContextPtr /* context */, const String & t
     return local_tables_cache[table_name].second;
 }
 
+void DatabaseMySQL::alterDatabaseComment(const AlterCommand & command)
+{
+    DB::updateDatabaseCommentWithMetadataFile(shared_from_this(), command);
+}
+
 String DatabaseMySQL::getMetadataPath() const
 {
     return metadata_path;

src/Databases/MySQL/DatabaseMySQL.h

@@ -26,7 +26,8 @@ namespace DB
 {
 
 class Context;
-
+struct AlterCommand;
+struct MySQLSettings;
 enum class MySQLDataTypesSupport : uint8_t;
 
 /** Real-time access to table list and table structure from remote MySQL
@@ -86,6 +87,8 @@ class DatabaseMySQL final : public IDatabase, WithContext
 
     void attachTable(ContextPtr context, const String & table_name, const StoragePtr & storage, const String & relative_table_path) override;
 
+    void alterDatabaseComment(const AlterCommand & command) override;
+
 protected:
     ASTPtr getCreateTableQueryImpl(const String & name, ContextPtr context, bool throw_on_error) const override;
 

src/Databases/PostgreSQL/DatabasePostgreSQL.cpp

@@ -6,9 +6,11 @@
 
 #include <DataTypes/DataTypeNullable.h>
 #include <DataTypes/DataTypeArray.h>
+#include <Storages/AlterCommands.h>
 #include <Storages/NamedCollectionsHelpers.h>
 #include <Storages/StoragePostgreSQL.h>
 #include <Interpreters/Context.h>
+#include <Interpreters/DatabaseCatalog.h>
 #include <Interpreters/evaluateConstantExpression.h>
 #include <Parsers/ASTCreateQuery.h>
 #include <Parsers/ASTFunction.h>
@@ -385,6 +387,10 @@ void DatabasePostgreSQL::shutdown()
     cleaner_task->deactivate();
 }
 
+void DatabasePostgreSQL::alterDatabaseComment(const AlterCommand & command)
+{
+    DB::updateDatabaseCommentWithMetadataFile(shared_from_this(), command);
+}
 
 ASTPtr DatabasePostgreSQL::getCreateDatabaseQuery() const
 {

src/Databases/PostgreSQL/DatabasePostgreSQL.h

@@ -13,6 +13,7 @@ namespace DB
 {
 
 class Context;
+struct AlterCommand;
 
 
 /** Real-time access to table list and table structure from remote PostgreSQL.
@@ -60,6 +61,8 @@ class DatabasePostgreSQL final : public IDatabase, WithContext
     void drop(ContextPtr /*context*/) override;
     void shutdown() override;
 
+    void alterDatabaseComment(const AlterCommand & command) override;
+
 protected:
     ASTPtr getCreateTableQueryImpl(const String & table_name, ContextPtr context, bool throw_on_error) const override;
 

src/Databases/SQLite/DatabaseSQLite.cpp

@@ -2,12 +2,14 @@
 
 #if USE_SQLITE
 
+#include <Storages/AlterCommands.h>
 #include <Common/logger_useful.h>
 #include <Core/Settings.h>
 #include <DataTypes/DataTypesNumber.h>
 #include <DataTypes/DataTypeNullable.h>
 #include <Databases/DatabaseFactory.h>
 #include <Databases/SQLite/fetchSQLiteTableStructure.h>
+#include <Interpreters/DatabaseCatalog.h>
 #include <Parsers/ASTCreateQuery.h>
 #include <Parsers/ASTColumnDeclaration.h>
 #include <Parsers/ASTFunction.h>
@@ -173,6 +175,10 @@ ASTPtr DatabaseSQLite::getCreateDatabaseQuery() const
     return create_query;
 }
 
+void DatabaseSQLite::alterDatabaseComment(const AlterCommand & command)
+{
+    DB::updateDatabaseCommentWithMetadataFile(shared_from_this(), command);
+}
 
 ASTPtr DatabaseSQLite::getCreateTableQueryImpl(const String & table_name, ContextPtr local_context, bool throw_on_error) const
 {

src/Databases/SQLite/DatabaseSQLite.h

@@ -12,6 +12,8 @@
 
 namespace DB
 {
+struct AlterCommand;
+
 class DatabaseSQLite final : public IDatabase, WithContext
 {
 public:
@@ -40,6 +42,8 @@ class DatabaseSQLite final : public IDatabase, WithContext
 
     void shutdown() override {}
 
+    void alterDatabaseComment(const AlterCommand & command) override;
+
 protected:
     ASTPtr getCreateTableQueryImpl(const String & table_name, ContextPtr context, bool throw_on_error) const override;