chore(query): add DistinctToGroupBy

src/query/ast/src/lib.rs

@@ -28,6 +28,7 @@ pub use visitors::walk_expr;
 pub use visitors::walk_expr_mut;
 pub use visitors::walk_query;
 pub use visitors::walk_query_mut;
+pub use visitors::walk_statement_mut;
 pub use visitors::Visitor;
 pub use visitors::VisitorMut;
 

src/query/ast/src/visitors/visitor_mut.rs

@@ -344,7 +344,9 @@ pub trait VisitorMut: Sized {
         walk_query_mut(self, query);
     }
 
-    fn visit_explain(&mut self, _kind: &mut ExplainKind, _query: &mut Statement<'_>) {}
+    fn visit_explain(&mut self, _kind: &mut ExplainKind, stmt: &mut Statement<'_>) {
+        walk_statement_mut(self, stmt);
+    }
 
     fn visit_copy(&mut self, _copy: &mut CopyStmt<'_>) {}
 

src/query/sql/src/planner/planner.rs

@@ -14,16 +14,19 @@
 
 use std::sync::Arc;
 
+use common_ast::ast::Statement;
 use common_ast::parser::parse_sql;
 use common_ast::parser::token::Token;
 use common_ast::parser::token::TokenKind;
 use common_ast::parser::token::Tokenizer;
+use common_ast::walk_statement_mut;
 use common_ast::Backtrace;
 use common_catalog::catalog::CatalogManager;
 use common_catalog::table_context::TableContext;
 use common_exception::Result;
 use parking_lot::RwLock;
 
+use super::semantic::DistinctToGroupBy;
 use crate::optimizer::optimize;
 use crate::optimizer::OptimizerConfig;
 use crate::optimizer::OptimizerContext;
@@ -76,8 +79,8 @@ impl Planner {
             let res = async {
                 // Step 2: Parse the SQL.
                 let backtrace = Backtrace::new();
-                let (stmt, format) = parse_sql(&tokens, sql_dialect, &backtrace)?;
-
+                let (mut stmt, format) = parse_sql(&tokens, sql_dialect, &backtrace)?;
+                replace_stmt(&mut stmt);
                 // Step 3: Bind AST with catalog, and generate a pure logical SExpr
                 let metadata = Arc::new(RwLock::new(Metadata::default()));
                 let name_resolution_ctx = NameResolutionContext::try_from(settings.as_ref())?;
@@ -126,3 +129,10 @@ impl Planner {
         }
     }
 }
+
+fn replace_stmt(stmt: &mut Statement) {
+    let mut visitors = vec![DistinctToGroupBy::default()];
+    for v in visitors.iter_mut() {
+        walk_statement_mut(v, stmt)
+    }
+}

src/query/sql/src/planner/semantic/distinct_to_groupby.rs

@@ -0,0 +1,105 @@
+// 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 common_ast::ast::Expr;
+use common_ast::ast::Identifier;
+use common_ast::ast::Query;
+use common_ast::ast::SelectStmt;
+use common_ast::ast::SetExpr;
+use common_ast::ast::TableReference;
+use common_ast::VisitorMut;
+
+#[derive(Debug, Clone, Default)]
+pub struct DistinctToGroupBy {}
+
+impl VisitorMut for DistinctToGroupBy {
+    fn visit_select_stmt(&mut self, stmt: &mut SelectStmt<'_>) {
+        let SelectStmt {
+            select_list,
+            from,
+            selection,
+            group_by,
+            having,
+            ..
+        } = stmt;
+
+        if group_by.is_empty() && select_list.len() == 1 && from.len() == 1 {
+            if let common_ast::ast::SelectTarget::AliasedExpr {
+                expr:
+                    box Expr::FunctionCall {
+                        span,
+                        distinct,
+                        name,
+                        args,
+                        ..
+                    },
+                alias,
+            } = &select_list[0]
+            {
+                if ((name.name.to_ascii_lowercase() == "count" && *distinct)
+                    || name.name.to_ascii_lowercase() == "count_distinct")
+                    && args.iter().all(|arg| !matches!(arg, Expr::Literal { .. }))
+                {
+                    let tmp_token = span[0].clone();
+                    let subquery = Query {
+                        span: &[],
+                        with: None,
+                        body: SetExpr::Select(Box::new(SelectStmt {
+                            span: &[],
+                            distinct: false,
+                            select_list: vec![],
+                            from: from.clone(),
+                            selection: None,
+                            group_by: args.clone(),
+                            having: None,
+                        })),
+                        order_by: vec![],
+                        limit: vec![],
+                        offset: None,
+                        ignore_result: false,
+                    };
+
+                    let new_stmt = SelectStmt {
+                        span: &[],
+                        distinct: false,
+                        select_list: vec![common_ast::ast::SelectTarget::AliasedExpr {
+                            expr: Box::new(Expr::FunctionCall {
+                                span: &[],
+                                distinct: false,
+                                name: Identifier {
+                                    name: "count".to_string(),
+                                    quote: None,
+                                    span: tmp_token.clone(),
+                                },
+                                args: vec![],
+                                params: vec![],
+                            }),
+                            alias: alias.clone(),
+                        }],
+                        from: vec![TableReference::Subquery {
+                            span: &[],
+                            subquery: Box::new(subquery),
+                            alias: None,
+                        }],
+                        selection: selection.clone(),
+                        group_by: vec![],
+                        having: having.clone(),
+                    };
+
+                    *stmt = new_stmt;
+                }
+            }
+        }
+    }
+}

src/query/sql/src/planner/semantic/mod.rs

@@ -12,11 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+mod distinct_to_groupby;
 mod grouping_check;
 mod lowering;
 mod name_resolution;
 mod type_check;
 
+pub use distinct_to_groupby::DistinctToGroupBy;
 pub use grouping_check::GroupingChecker;
 pub use name_resolution::compare_table_name;
 pub use name_resolution::normalize_identifier;

tests/sqllogictests/suites/mode/standalone/explain/explain.test

@@ -768,6 +768,70 @@ HashJoin
     ├── push downs: [filters: [], limit: NONE]
     └── estimated rows: 5.00
 
+query T
+explain select count(distinct a) from t1;
+----
+EvalScalar
+├── expressions: [count() (#3)]
+├── estimated rows: 1.00
+└── AggregateFinal
+    ├── group by: []
+    ├── aggregate functions: [count()]
+    ├── estimated rows: 1.00
+    └── AggregatePartial
+        ├── group by: []
+        ├── aggregate functions: [count()]
+        ├── estimated rows: 1.00
+        └── AggregateFinal
+            ├── group by: [a]
+            ├── aggregate functions: []
+            ├── estimated rows: 1.00
+            └── AggregatePartial
+                ├── group by: [a]
+                ├── aggregate functions: []
+                ├── estimated rows: 1.00
+                └── TableScan
+                    ├── table: default.default.t1
+                    ├── read rows: 1
+                    ├── read bytes: 31
+                    ├── partitions total: 1
+                    ├── partitions scanned: 1
+                    ├── push downs: [filters: [], limit: NONE]
+                    ├── output columns: [0]
+                    └── estimated rows: 1.00
+
+query T
+explain select count_distinct(a) from t1;
+----
+EvalScalar
+├── expressions: [count() (#3)]
+├── estimated rows: 1.00
+└── AggregateFinal
+    ├── group by: []
+    ├── aggregate functions: [count()]
+    ├── estimated rows: 1.00
+    └── AggregatePartial
+        ├── group by: []
+        ├── aggregate functions: [count()]
+        ├── estimated rows: 1.00
+        └── AggregateFinal
+            ├── group by: [a]
+            ├── aggregate functions: []
+            ├── estimated rows: 1.00
+            └── AggregatePartial
+                ├── group by: [a]
+                ├── aggregate functions: []
+                ├── estimated rows: 1.00
+                └── TableScan
+                    ├── table: default.default.t1
+                    ├── read rows: 1
+                    ├── read bytes: 31
+                    ├── partitions total: 1
+                    ├── partitions scanned: 1
+                    ├── push downs: [filters: [], limit: NONE]
+                    ├── output columns: [0]
+                    └── estimated rows: 1.00
+
 statement ok
 drop table t1