save TO table of a materialized view to the ATTACH query [#CLICKHOUSE-2]

dbms/src/Databases/DatabasesCommon.cpp

@@ -27,6 +27,8 @@ String getTableDefinitionFromCreateQuery(const ASTPtr & query)
     /// We remove everything that is not needed for ATTACH from the query.
     create.attach = true;
     create.database.clear();
+    create.as_database.clear();
+    create.as_table.clear();
     create.if_not_exists = false;
     create.is_populate = false;
 
@@ -34,13 +36,6 @@ String getTableDefinitionFromCreateQuery(const ASTPtr & query)
     if (!create.is_view && !create.is_materialized_view)
         create.select = nullptr;
 
-    /// For "MATERIALIZED VIEW x TO y" it's necessary to save destination table
-    if (!create.is_materialized_view || create.storage)
-    {
-        create.as_database.clear();
-        create.as_table.clear();
-    }
-
     std::ostringstream statement_stream;
     formatAST(create, statement_stream, 0, false);
     statement_stream << '\n';

dbms/src/Interpreters/InterpreterCreateQuery.cpp

@@ -480,12 +480,15 @@ BlockIO InterpreterCreateQuery::createTable(ASTCreateQuery & create)
         create.attach = true;
     }
 
+    if (create.to_database.empty())
+        create.to_database = current_database;
+
     std::unique_ptr<InterpreterSelectQuery> interpreter_select;
     Block as_select_sample;
     /// For `view` type tables, you may need `sample_block` to get the columns.
     if (create.select && (!create.attach || (!create.columns && (create.is_view || create.is_materialized_view))))
     {
-        create.select->setDatabaseIfNeeded(database_name);
+        create.select->setDatabaseIfNeeded(current_database);
         interpreter_select = std::make_unique<InterpreterSelectQuery>(create.select->ptr(), context);
         as_select_sample = interpreter_select->getSampleBlock();
     }

dbms/src/Parsers/ASTCreateQuery.h

@@ -88,6 +88,8 @@ public:
     String database;
     String table;
     ASTExpressionList * columns = nullptr;
+    String to_database;   /// For CREATE MATERIALIZED VIEW mv TO table.
+    String to_table;
     ASTStorage * storage = nullptr;
     String as_database;
     String as_table;
@@ -166,11 +168,18 @@ protected:
                 formatOnCluster(settings);
         }
 
+        if (!to_table.empty())
+        {
+            settings.ostr
+                << (settings.hilite ? hilite_keyword : "") << " TO " << (settings.hilite ? hilite_none : "")
+                << (!to_database.empty() ? backQuoteIfNeed(to_database) + "." : "") << backQuoteIfNeed(to_table);
+        }
+
         if (!as_table.empty())
         {
-            std::string what = (!is_materialized_view ? " AS " : " TO ");
-            settings.ostr << (settings.hilite ? hilite_keyword : "") << what << (settings.hilite ? hilite_none : "")
-            << (!as_database.empty() ? backQuoteIfNeed(as_database) + "." : "") << backQuoteIfNeed(as_table);
+            settings.ostr
+                << (settings.hilite ? hilite_keyword : "") << " AS " << (settings.hilite ? hilite_none : "")
+                << (!as_database.empty() ? backQuoteIfNeed(as_database) + "." : "") << backQuoteIfNeed(as_table);
         }
 
         if (columns)

dbms/src/Parsers/ParserCreateQuery.cpp

@@ -208,6 +208,8 @@ bool ParserCreateQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
     ASTPtr database;
     ASTPtr table;
     ASTPtr columns;
+    ASTPtr to_database;
+    ASTPtr to_table;
     ASTPtr storage;
     ASTPtr as_database;
     ASTPtr as_table;
@@ -219,7 +221,6 @@ bool ParserCreateQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
     bool is_materialized_view = false;
     bool is_populate = false;
     bool is_temporary = false;
-    bool to_table = false;
 
     if (!s_create.ignore(pos, expected))
     {
@@ -362,17 +363,13 @@ bool ParserCreateQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
         // TO [db.]table
         if (ParserKeyword{"TO"}.ignore(pos, expected))
         {
-            to_table = true;
-
-            /// FIXME: as_table is ambiguous, it is set in AS clause also
-
-            if (!name_p.parse(pos, as_table, expected))
+            if (!name_p.parse(pos, to_table, expected))
                 return false;
 
             if (s_dot.ignore(pos, expected))
             {
-                as_database = as_table;
-                if (!name_p.parse(pos, as_table, expected))
+                to_database = to_table;
+                if (!name_p.parse(pos, to_table, expected))
                     return false;
             }
         }
@@ -422,6 +419,11 @@ bool ParserCreateQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
         query->table = typeid_cast<ASTIdentifier &>(*table).name;
     query->cluster = cluster_str;
 
+    if (to_database)
+        query->to_database = typeid_cast<ASTIdentifier &>(*to_database).name;
+    if (to_table)
+        query->to_table = typeid_cast<ASTIdentifier &>(*to_table).name;
+
     query->set(query->columns, columns);
     query->set(query->storage, storage);
     if (as_database)

dbms/src/Storages/StorageFactory.cpp

@@ -388,9 +388,6 @@ StoragePtr StorageFactory::get(
     checkAllTypesAreAllowedInTable(materialized_columns);
     checkAllTypesAreAllowedInTable(alias_columns);
 
-    if (!query.storage)
-        throw Exception("Incorrect CREATE query: ENGINE required", ErrorCodes::ENGINE_REQUIRED);
-
     if (query.is_materialized_view)
     {
         /// Pass local_context here to convey setting for inner table
@@ -400,6 +397,9 @@ StoragePtr StorageFactory::get(
             attach);
     }
 
+    if (!query.storage)
+        throw Exception("Incorrect CREATE query: ENGINE required", ErrorCodes::ENGINE_REQUIRED);
+
     ASTStorage & storage_def = *query.storage;
     const ASTFunction & engine_def = *storage_def.engine;
 
@@ -423,7 +423,7 @@ StoragePtr StorageFactory::get(
 
     auto check_arguments_empty = [&]
     {
-        if (args_ptr)
+        if (args_ptr && !args_ptr->empty())
             throw Exception(
                 "Engine " + name + " doesn't support any arguments (" + toString(args_ptr->size()) + " given)",
                 ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

dbms/src/Storages/StorageMaterializedView.cpp

@@ -70,8 +70,10 @@ StorageMaterializedView::StorageMaterializedView(
     if (!query.select)
         throw Exception("SELECT query is not specified for " + getName(), ErrorCodes::INCORRECT_QUERY);
 
-    if (!query.storage && query.as_table.empty())
-        throw Exception("ENGINE of MaterializedView should be specified explicitly", ErrorCodes::INCORRECT_QUERY);
+    if (!query.storage && query.to_table.empty())
+        throw Exception(
+            "You must specify where to save results of a MaterializedView query: either ENGINE or an existing table in a TO clause",
+            ErrorCodes::INCORRECT_QUERY);
 
     extractDependentTable(*query.select, select_database_name, select_table_name);
 
@@ -81,10 +83,10 @@ StorageMaterializedView::StorageMaterializedView(
             DatabaseAndTableName(database_name, table_name));
 
     // If the destination table is not set, use inner table
-    if (!query.as_table.empty())
+    if (!query.to_table.empty())
     {
-        target_database_name = query.as_database;
-        target_table_name = query.as_table;
+        target_database_name = query.to_database;
+        target_table_name = query.to_table;
     }
     else
     {

dbms/tests/queries/0_stateless/00508_materialized_view_to.reference

@@ -2,3 +2,9 @@
 2
 1
 2
+1
+2
+3
+1
+2
+3

dbms/tests/queries/0_stateless/00508_materialized_view_to.sql

@@ -5,16 +5,26 @@ DROP TABLE IF EXISTS test.mv;
 CREATE TABLE test.src (x UInt8) ENGINE = Null;
 CREATE TABLE test.dst (x UInt8) ENGINE = Memory;
 
-CREATE MATERIALIZED VIEW test.mv TO test.dst AS SELECT * FROM test.src;
-INSERT INTO test.src VALUES (1), (2);
+USE test;
+
+CREATE MATERIALIZED VIEW mv TO dst AS SELECT * FROM src;
+
+INSERT INTO src VALUES (1), (2);
+SELECT * FROM mv;
 
 -- Detach MV and see if the data is still readable
-DETACH TABLE test.mv;
-SELECT * FROM test.dst;
+DETACH TABLE mv;
+SELECT * FROM dst;
+
+USE default;
 
 -- Reattach MV (shortcut)
 ATTACH TABLE test.mv;
 
+INSERT INTO test.src VALUES (3);
+
+SELECT * FROM test.mv;
+
 -- Drop the MV and see if the data is still readable
 DROP TABLE test.mv;
 SELECT * FROM test.dst;