andygrove commented on code in PR #3884:
URL: https://github.com/apache/arrow-datafusion/pull/3884#discussion_r998720316
##########
datafusion/expr/src/expr.rs:
##########
@@ -267,6 +267,28 @@ impl BinaryExpr {
}
}
+impl Display for BinaryExpr {
+ fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+ // Put parentheses around child binary expressions so that we can see
the difference
+ // between `(a OR b) AND c` and `a OR (b AND c)`. A future improvement
here would be
+ // to only insert parentheses when needed, based on operator
precedence. For example,
+ // `(a AND b) OR c` and `a AND b OR c` are equivalent and the
parentheses are not
+ // necessary
+ if matches!(*self.left, Expr::BinaryExpr(_)) {
+ write!(f, "({})", self.left)?;
+ } else {
+ write!(f, "{}", self.left)?;
+ }
+ write!(f, " {} ", self.op)?;
+ if matches!(*self.right, Expr::BinaryExpr(_)) {
+ write!(f, "({})", self.right)?;
+ } else {
+ write!(f, "{}", self.right)?;
+ }
+ Ok(())
+ }
+}
Review Comment:
I am torn between doing the bare minimum (the current PR changes) and
implementing this fully with operator precedence. This would be much more work,
and we would need comprehensive tests. Maybe there is some middle ground where
we respect operator precedence for the common cases (AND/OR and +.-.*./) and
just wrap anything else in parentheses. We can then improve this over time.
I'll try this approach tomorrow.
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