add explain to sql parser

src/datanode/src/instance/sql.rs

@@ -115,6 +115,9 @@ impl Instance {
             Statement::ShowTables(stmt) => {
                 self.sql_handler.execute(SqlRequest::ShowTables(stmt)).await
             }
+            Statement::Explain(_explain) => {
+                unimplemented!()
+            }
             Statement::ShowCreateTable(_stmt) => {
                 unimplemented!("SHOW CREATE TABLE is unimplemented yet");
             }

src/frontend/src/instance.rs

@@ -272,6 +272,11 @@ impl Instance {
             .context(AlterTableSnafu)
     }
 
+    /// Handle explain expr
+    pub async fn handle_explain(&self) -> Result<Output> {
+        todo!()
+    }
+
     /// Handle batch inserts
     pub async fn handle_inserts(&self, insert_expr: &[InsertExpr]) -> Result<Output> {
         let mut success = 0;
@@ -624,6 +629,10 @@ impl SqlQueryHandler for Instance {
                 .await
                 .map_err(BoxedError::new)
                 .context(server_error::ExecuteQuerySnafu { query }),
+            Statement::Explain(_explain) => {
+                // self.handle_explain()
+                unimplemented!()
+            }
             Statement::ShowCreateTable(_) => {
                 return server_error::NotSupportedSnafu { feat: query }.fail()
             }

src/query/src/datafusion/planner.rs

@@ -69,6 +69,7 @@ where
             | Statement::CreateTable(_)
             | Statement::CreateDatabase(_)
             | Statement::Alter(_)
+            | Statement::Explain(_)
             | Statement::Insert(_) => unreachable!(),
         }
     }

src/sql/src/parser.rs

@@ -21,8 +21,9 @@ use sqlparser::tokenizer::{Token, Tokenizer};
 use crate::error::{
     self, InvalidDatabaseNameSnafu, InvalidTableNameSnafu, Result, SyntaxSnafu, TokenizerSnafu,
 };
+use crate::statements::explain::Explain;
 use crate::statements::show::{ShowCreateTable, ShowDatabases, ShowKind, ShowTables};
-use crate::statements::statement::Statement;
+use crate::statements::statement::*;
 
 /// GrepTime SQL parser context, a simple wrapper for Datafusion SQL parser.
 pub struct ParserContext<'a> {
@@ -218,7 +219,34 @@ impl<'a> ParserContext<'a> {
     }
 
     fn parse_explain(&mut self) -> Result<Statement> {
-        todo!()
+        let has_describe_alias = match self.parser.next_token() {
+            Token::Word(word) => match word.keyword {
+                Keyword::DESC => true,
+                Keyword::DESCRIBE => true,
+                _ => false,
+            },
+            _ => false,
+        };
+
+        let explain_statement = if has_describe_alias {
+            self.parser
+                .parse_explain(false)
+                .with_context(|_| error::UnexpectedSnafu {
+                    sql: self.sql,
+                    expected: "a statement",
+                    actual: self.peek_token_as_string(),
+                })?
+        } else {
+            self.parser
+                .parse_explain(false)
+                .with_context(|_| error::UnexpectedSnafu {
+                    sql: self.sql,
+                    expected: "a statement",
+                    actual: self.peek_token_as_string(),
+                })?
+        };
+
+        Ok(Statement::Explain(Explain::try_from(explain_statement)?))
     }
 
     // Report unexpected token

src/sql/src/statements.rs

@@ -14,6 +14,7 @@
 
 pub mod alter;
 pub mod create;
+pub mod explain;
 pub mod insert;
 pub mod query;
 pub mod show;

src/sql/src/statements/explain.rs

@@ -0,0 +1,31 @@
+// Copyright 2022 Greptime Team
+//
+// 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 sqlparser::ast::Statement;
+
+/// Explain statement instance.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Explain {
+    pub inner: Statement,
+}
+
+use crate::error::Error;
+
+impl TryFrom<Statement> for Explain {
+    type Error = Error;
+
+    fn try_from(value: Statement) -> Result<Self, Self::Error> {
+        Ok(Explain { inner: value })
+    }
+}

src/sql/src/statements/statement.rs

@@ -17,6 +17,7 @@ use sqlparser::parser::ParserError;
 
 use crate::statements::alter::AlterTable;
 use crate::statements::create::{CreateDatabase, CreateTable};
+use crate::statements::explain::Explain;
 use crate::statements::insert::Insert;
 use crate::statements::query::Query;
 use crate::statements::show::{ShowCreateTable, ShowDatabases, ShowTables};
@@ -40,6 +41,8 @@ pub enum Statement {
     ShowTables(ShowTables),
     // SHOW CREATE TABLE
     ShowCreateTable(ShowCreateTable),
+    // EXPLAIN [[ DESCRIBE| DESC ]] select_statement
+    Explain(Explain),
 }
 
 /// Converts Statement to sqlparser statement
@@ -62,6 +65,7 @@ impl TryFrom<Statement> for SpStatement {
             Statement::CreateDatabase(_) | Statement::CreateTable(_) | Statement::Alter(_) => {
                 unimplemented!()
             }
+            Statement::Explain(e) => Ok(e.inner),
         }
     }
 }