yyy1000 commented on code in PR #8780:
URL: https://github.com/apache/arrow-datafusion/pull/8780#discussion_r1444797946
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datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs:
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@@ -224,6 +226,63 @@ impl<S: SimplifyInfo> ExprSimplifier<S> {
}
}
+#[allow(rustdoc::private_intra_doc_links)]
+/// Canonicalize any BinaryExprs that are not in canonical form
+/// <literal> <op> <col> is rewritten to <col> <op> <literal> (remember to
switch the operator)
+/// <col> <op> <literal> is canonical
+/// <col1> <op> <col2> is rewritten so that the name of col1 sorts higher than
col2 (b > a would be canonicalized to a < b)
+struct Canonicalizer {}
+
+impl Canonicalizer {
+ fn new() -> Self {
+ Self {}
+ }
+}
+
+impl TreeNodeRewriter for Canonicalizer {
+ type N = Expr;
+
+ fn mutate(&mut self, expr: Expr) -> Result<Expr> {
+ if let Expr::BinaryExpr(BinaryExpr { left, op, right }) = expr {
+ // Case 1, <col1> <op> <col2>
+ let mut new_expr = BinaryExpr {
+ left: left.clone(),
+ op: op.clone(),
+ right: right.clone(),
+ };
+ let mut switch_op: Operator = op.clone();
+ if left.try_into_col().is_ok() && right.try_into_col().is_ok() {
+ let left_name = left.canonical_name();
+ let right_name = right.canonical_name();
+ if left_name < right_name {
+ if let Some(swap_op) = op.swap() {
+ switch_op = swap_op;
+ }
Review Comment:
Got it.
Here `swap` would return None if operator makes no sense, e.g.: `-`, see:
https://github.com/apache/arrow-datafusion/blob/cc4289484c33e478242bf5d2b59f695fdb427ab9/datafusion/expr/src/operator.rs#L172C5-L202C6
I think in this case we will not change the order of the Expr, and <col1>
and <col2> would remain the same order as before.
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