comphead commented on code in PR #10431:
URL: https://github.com/apache/datafusion/pull/10431#discussion_r1598637244
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datafusion/optimizer/src/eliminate_cross_join.rs:
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@@ -39,102 +41,147 @@ impl EliminateCrossJoin {
}
}
-/// Attempt to reorder join to eliminate cross joins to inner joins.
-/// for queries:
-/// 'select ... from a, b where a.x = b.y and b.xx = 100;'
-/// 'select ... from a, b where (a.x = b.y and b.xx = 100) or (a.x = b.y and
b.xx = 200);'
-/// 'select ... from a, b, c where (a.x = b.y and b.xx = 100 and a.z = c.z)
-/// or (a.x = b.y and b.xx = 200 and a.z=c.z);'
-/// 'select ... from a, b where a.x > b.y'
+/// Eliminate cross joins by rewriting them to inner joins when possible.
+///
+/// # Example
+/// The initial plan for this query:
+/// ```sql
+/// select ... from a, b where a.x = b.y and b.xx = 100;
+/// ```
+///
+/// Looks like this:
+/// ```text
+/// Filter(a.x = b.y AND b.xx = 100)
+/// CrossJoin
+/// TableScan a
+/// TableScan b
+/// ```
+///
+/// After the rule is applied, the plan will look like this:
+/// ```text
+/// Filter(b.xx = 100)
Review Comment:
I hope the pushdown filter predicate rule comes after this rule
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