alamb commented on a change in pull request #1128:
URL: https://github.com/apache/arrow-datafusion/pull/1128#discussion_r731283571
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File path: datafusion/src/optimizer/utils.rs
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@@ -468,6 +473,117 @@ pub fn rewrite_expression(expr: &Expr, expressions:
&[Expr]) -> Result<Expr> {
}
}
+///Tests an expression to see if it contains only literal expressions such as
3+4.5 and immutable scalar builtins or UDFs.
+pub fn expr_is_const(expr: &Expr) -> bool {
+ match expr {
+ Expr::Column(_)
+ | Expr::ScalarVariable(_)
+ | Expr::AggregateFunction { .. }
+ | Expr::WindowFunction { .. }
+ | Expr::AggregateUDF { .. }
+ | Expr::Sort { .. }
+ | Expr::Wildcard => false,
+
+ Expr::Literal(_) => true,
+
+ Expr::Alias(child, _)
+ | Expr::Not(child)
+ | Expr::IsNotNull(child)
+ | Expr::IsNull(child)
+ | Expr::Negative(child)
+ | Expr::Cast { expr: child, .. }
+ | Expr::TryCast { expr: child, .. } => expr_is_const(child),
+
+ Expr::ScalarFunction { fun, args } => match fun.volatility() {
+ Volatility::Immutable => args.iter().all(|arg| expr_is_const(arg)),
+ Volatility::Stable | Volatility::Volatile => false,
+ },
+ Expr::BinaryExpr { left, right, .. } => {
+ expr_is_const(left) && expr_is_const(right)
+ }
+ Expr::Between {
+ expr, low, high, ..
+ } => expr_is_const(expr) && expr_is_const(low) && expr_is_const(high),
+ Expr::Case {
+ expr,
+ when_then_expr,
+ else_expr,
+ } => {
+ let expr_constant = expr.as_ref().map(|e|
expr_is_const(e)).unwrap_or(true);
+ let else_constant =
+ else_expr.as_ref().map(|e| expr_is_const(e)).unwrap_or(true);
+ let when_then_constant = when_then_expr
+ .iter()
+ .all(|(w, th)| expr_is_const(w) && expr_is_const(th));
+ expr_constant && else_constant && when_then_constant
+ }
+
+ Expr::ScalarUDF { fun, args } => match fun.volatility() {
+ Volatility::Immutable => args.iter().all(|arg| expr_is_const(arg)),
+ Volatility::Stable | Volatility::Volatile => false,
+ },
+
+ Expr::InList { expr, list, .. } => {
+ expr_is_const(expr) && list.iter().all(|e| expr_is_const(e))
+ }
+ }
+}
+
+///Evaluates an expression if it only contains literal expressions. If a
non-literal expression or non-immutable function is found then it returns an
error.
Review comment:
I suggest the public API should be something like:
```rust
partially_evaluate_expr(expr: &Expr)
```
or
```rust
Expr::partially_evaluate(self) -> Self
```
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