izveigor commented on code in PR #5816:
URL: https://github.com/apache/arrow-datafusion/pull/5816#discussion_r1154823149
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datafusion/optimizer/src/simplify_expressions/utils.rs:
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@@ -350,6 +351,73 @@ pub fn distribute_negation(expr: Expr) -> Expr {
}
}
+/// Simplify the `log` function by the relevant rules:
+/// 1. Log(a, 1) ===> 0
+/// 2. Log(a, a) ===> 1
+/// 3. Log(a, Power(a, b)) ===> b
+pub fn simpl_log(current_args: Vec<Expr>, info: &dyn SimplifyInfo) ->
Result<Expr> {
+ let base = ¤t_args[0];
+ let number = ¤t_args[1];
+
+ match number {
+ Expr::Literal(value)
+ if value == &ScalarValue::new_one(&info.get_data_type(number)?)? =>
+ {
+ Ok(Expr::Literal(ScalarValue::new_zero(
+ &info.get_data_type(base)?,
+ )?))
+ }
+ Expr::ScalarFunction {
+ fun: BuiltinScalarFunction::Power,
+ args,
+ } if base == &args[0] => Ok(args[1].clone()),
+ _ => {
+ if number == base {
+ Ok(Expr::Literal(ScalarValue::new_one(
+ &info.get_data_type(number)?,
+ )?))
+ } else {
+ Ok(Expr::ScalarFunction {
+ fun: BuiltinScalarFunction::Log,
+ args: current_args,
+ })
+ }
+ }
+ }
+}
+
+/// Simplify the `power` function by the relevant rules:
+/// 1. Power(a, 0) ===> 0
+/// 2. Power(a, 1) ===> a
+/// 3. Power(a, Log(a, b)) ===> b
Review Comment:
Should we use the law: Power(a1, a2*a3*a4*Log(a1, a5)) ===> a2*a3*a4*a5? 🤔
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