xanderbailey commented on code in PR #17299:
URL: https://github.com/apache/datafusion/pull/17299#discussion_r2323660433
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datafusion/substrait/src/logical_plan/consumer/rel/project_rel.rs:
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@@ -62,7 +62,17 @@ pub async fn from_project_rel(
// to transform it into a column reference
window_exprs.insert(e.clone());
}
- explicit_exprs.push(name_tracker.get_uniquely_named_expr(e)?);
+ // Since substrait removes aliases, we need to assign literals
with a UUID alias to avoid
+ // ambiguous names when the same literal is used before and after
a join.
+ // The name tracker will ensure that two literals in the same
project would have
+ // unique names but, it does not ensure that if a literal column
exists in a previous
+ // project say before a join that it is deduplicated with respect
to those columns.
Review Comment:
Yes so the name tracker makes sure that if you have a project that creates
two null string columns, it will create two unique names for those two columns.
But, say you create one of those null columns before a join and then another in
a project immediately after a join, the plan fails with an ambiguous column
error because there is a UTF8(NULL) from say the left and then another
UTF8(NULL) from the project after the join which has no source and it's
therefore an ambiguous reference.
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