risingwave_frontend/optimizer/plan_expr_visitor/
expr_counter.rs

1// Copyright 2025 RisingWave Labs
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15use std::collections::HashMap;
16
17use crate::expr::{ExprImpl, ExprType, ExprVisitor, FunctionCall, default_visit_expr};
18
19/// `ExprCounter` is used by `CseRewriter`.
20#[derive(Default)]
21pub struct CseExprCounter {
22    // Only count pure function call and not const.
23    pub counter: HashMap<FunctionCall, usize>,
24}
25
26impl ExprVisitor for CseExprCounter {
27    fn visit_expr(&mut self, expr: &ExprImpl) {
28        // Considering this sql, `In` expression needs to ensure its in-clauses to be const.
29        // If we extract it into a common sub-expression (finally be a `InputRef`) which will
30        // violate this assumption, so ban this case. SELECT x,
31        //        tand(x) IN ('-Infinity'::float8,-1,0,1,'Infinity'::float8) AS tand_exact,
32        //        cotd(x) IN ('-Infinity'::float8,-1,0,1,'Infinity'::float8) AS cotd_exact
33        // FROM (VALUES (0), (45), (90), (135), (180),(225), (270), (315), (360)) AS t(x);
34        if expr.is_const() {
35            return;
36        }
37
38        default_visit_expr(self, expr);
39    }
40
41    fn visit_function_call(&mut self, func_call: &FunctionCall) {
42        if func_call.is_pure() {
43            self.counter
44                .entry(func_call.clone())
45                .and_modify(|counter| *counter += 1)
46                .or_insert(1);
47        }
48
49        match func_call.func_type() {
50            // Short cut semantic func type cannot be extracted into common sub-expression.
51            // E.g. select case when a = 0 then 0 when a < 10 then 1 + 1 / a else 1 / a end from x
52            // If a is zero, common sub-expression (1 / a) would lead to division by zero error.
53            //
54            // Also note `AND`/`OR` is not guaranteed this semantic.
55            // E.g. select * from a, b where a1 > b1*b1 and 3 / a1 < 5;
56            // Optimizer is allowed to filter with `3 / a1 < 5` before join on `a1 > b1*b1`.
57            // This can lead to division by zero error not observed without optimization.
58            ExprType::Case | ExprType::Coalesce => {
59                return;
60            }
61            // `some` and `all` cannot be separated from their inner binary boolean operator #11766
62            // We could still visit the lhs scalar and rhs array, but keeping it simple here.
63            // E.g. `v not like some(arr)` is bound as `Some(Not(Like(v, arr)))`
64            // It is invalid to extract `Like(v, arr)` or `Not(Like(v, arr))`. `v` and `arr` are ok.
65            ExprType::Some | ExprType::All => {
66                return;
67            }
68            _ => {}
69        };
70
71        func_call
72            .inputs()
73            .iter()
74            .for_each(|expr| self.visit_expr(expr));
75    }
76}
risingwave_frontend/optimizer/plan_expr_visitor/expr_counter.rs

risingwave_frontend/optimizer/plan_expr_visitor/
expr_counter.rs
