ISSUE-4860: fix empty query

query/src/interpreters/interpreter_empty.rs

@@ -0,0 +1,53 @@
+// Copyright 2022 Datafuse Labs.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::sync::Arc;
+
+use common_datavalues::prelude::*;
+use common_exception::Result;
+use common_planners::EmptyPlan;
+use common_streams::DataBlockStream;
+use common_streams::SendableDataBlockStream;
+
+use crate::interpreters::Interpreter;
+use crate::interpreters::InterpreterPtr;
+use crate::sessions::QueryContext;
+
+// EmptyInterpreter is a Empty interpreter to execute nothing.
+// Such as the query '/*!40101*/', it makes the front-end (e.g. MySQL handler) no need check the EmptyPlan or not.
+pub struct EmptyInterpreter {}
+
+impl EmptyInterpreter {
+    pub fn try_create(_ctx: Arc<QueryContext>, _plan: EmptyPlan) -> Result<InterpreterPtr> {
+        Ok(Arc::new(EmptyInterpreter {}))
+    }
+}
+
+#[async_trait::async_trait]
+impl Interpreter for EmptyInterpreter {
+    fn name(&self) -> &str {
+        "EmptyInterpreter"
+    }
+
+    async fn execute(
+        &self,
+        _input_stream: Option<SendableDataBlockStream>,
+    ) -> Result<SendableDataBlockStream> {
+        Ok(Box::pin(DataBlockStream::create(
+            Arc::new(DataSchema::empty()),
+            None,
+            vec![],
+        )))
+    }
+}

query/src/interpreters/interpreter_factory.rs

@@ -43,6 +43,7 @@ use crate::interpreters::DropTableInterpreter;
 use crate::interpreters::DropUserInterpreter;
 use crate::interpreters::DropUserUDFInterpreter;
 use crate::interpreters::DropViewInterpreter;
+use crate::interpreters::EmptyInterpreter;
 use crate::interpreters::ExplainInterpreter;
 use crate::interpreters::GrantPrivilegeInterpreter;
 use crate::interpreters::GrantRoleInterpreter;
@@ -172,6 +173,7 @@ impl InterpreterFactory {
             PlanNode::UseDatabase(v) => UseDatabaseInterpreter::try_create(ctx_clone, v),
             PlanNode::Kill(v) => KillInterpreter::try_create(ctx_clone, v),
             PlanNode::SetVariable(v) => SettingInterpreter::try_create(ctx_clone, v),
+            PlanNode::Empty(v) => EmptyInterpreter::try_create(ctx_clone, v),
 
             _ => Result::Err(ErrorCode::UnknownTypeOfQuery(format!(
                 "Can't get the interpreter by plan:{}",

query/src/interpreters/mod.rs

@@ -19,6 +19,7 @@ mod interpreter_copy;
 mod interpreter_database_create;
 mod interpreter_database_drop;
 mod interpreter_database_show_create;
+mod interpreter_empty;
 mod interpreter_explain;
 mod interpreter_factory;
 mod interpreter_factory_interceptor;
@@ -76,6 +77,7 @@ pub use interpreter_copy::CopyInterpreter;
 pub use interpreter_database_create::CreateDatabaseInterpreter;
 pub use interpreter_database_drop::DropDatabaseInterpreter;
 pub use interpreter_database_show_create::ShowCreateDatabaseInterpreter;
+pub use interpreter_empty::EmptyInterpreter;
 pub use interpreter_explain::ExplainInterpreter;
 pub use interpreter_factory::InterpreterFactory;
 pub use interpreter_factory_interceptor::InterceptorInterpreter;

query/src/sql/plan_parser.rs

@@ -16,6 +16,7 @@ use std::sync::Arc;
 
 use common_exception::ErrorCode;
 use common_exception::Result;
+use common_planners::EmptyPlan;
 use common_planners::ExplainPlan;
 use common_planners::Expression;
 use common_planners::PlanBuilder;
@@ -54,7 +55,7 @@ impl PlanParser {
         ctx: Arc<QueryContext>,
     ) -> Result<PlanNode> {
         if statements.is_empty() {
-            return Err(ErrorCode::SyntaxException("Empty query"));
+            return Ok(PlanNode::Empty(EmptyPlan::create()));
         } else if statements.len() > 1 {
             return Err(ErrorCode::SyntaxException("Only support single query"));
         }

query/tests/it/interpreters/interpreter_empty.rs

@@ -0,0 +1,60 @@
+// Copyright 2021 Datafuse Labs.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use common_base::tokio;
+use common_exception::Result;
+use databend_query::interpreters::*;
+use databend_query::sql::*;
+use futures::TryStreamExt;
+use pretty_assertions::assert_eq;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn test_empty_interpreter() -> Result<()> {
+    common_tracing::init_default_ut_tracing();
+    let ctx = crate::tests::create_query_context().await?;
+
+    {
+        let query = "/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */";
+        let plan = PlanParser::parse(ctx.clone(), query).await?;
+        let executor = InterpreterFactory::get(ctx.clone(), plan)?;
+        assert_eq!(executor.name(), "EmptyInterpreter");
+
+        let stream = executor.execute(None).await?;
+        let result = stream.try_collect::<Vec<_>>().await;
+        assert!(result.is_ok())
+    }
+
+    {
+        let query = "/*!40101*/select number from numbers_mt(1)";
+        let plan = PlanParser::parse(ctx.clone(), query).await?;
+        let executor = InterpreterFactory::get(ctx.clone(), plan)?;
+        assert_eq!(executor.name(), "SelectInterpreter");
+
+        let stream = executor.execute(None).await?;
+        let result = stream.try_collect::<Vec<_>>().await?;
+        let block = &result[0];
+        assert_eq!(block.num_columns(), 1);
+
+        let expected = vec![
+            "+--------+",
+            "| number |",
+            "+--------+",
+            "| 0      |",
+            "+--------+",
+        ];
+        common_datablocks::assert_blocks_sorted_eq(expected, result.as_slice());
+    }
+
+    Ok(())
+}

query/tests/it/interpreters/mod.rs

@@ -16,6 +16,7 @@ mod interpreter_call;
 mod interpreter_database_create;
 mod interpreter_database_drop;
 mod interpreter_database_show_create;
+mod interpreter_empty;
 mod interpreter_explain;
 mod interpreter_factory_interceptor;
 mod interpreter_insert;

query/tests/it/servers/http/clickhouse_handler.rs

@@ -45,12 +45,6 @@ macro_rules! assert_ok {
 async fn test_select() -> PoemResult<()> {
     let server = Server::new();
 
-    {
-        let (status, body) = server.get("").await;
-        assert_eq!(status, StatusCode::BAD_REQUEST);
-        assert_error!(body, "Empty query");
-    }
-
     {
         let (status, body) = server.get("bad sql").await;
         assert_eq!(status, StatusCode::BAD_REQUEST);
@@ -69,6 +63,12 @@ async fn test_select() -> PoemResult<()> {
         assert_error!(body, "sql parser error");
     }
 
+    {
+        let (status, body) = server.get("").await;
+        assert_eq!(status, StatusCode::OK);
+        assert_eq!(&body, "");
+    }
+
     {
         let (status, body) = server.get("select 1").await;
         assert_eq!(status, StatusCode::OK);

tests/suites/0_stateless/03_dml/03_0019_select_empty.result

@@ -0,0 +1,3 @@
+0
+1
+0

tests/suites/0_stateless/03_dml/03_0019_select_empty.sql

@@ -0,0 +1,3 @@
+/*!40101*/select number from numbers_mt(2);
+/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
+/*!40101*/select number from numbers_mt(1);