xiedeyantu commented on PR #4897:
URL: https://github.com/apache/calcite/pull/4897#issuecomment-4613884911
Current PR Change Management Process:
1. `MinusMergeRule`
Merges the nested binary `Minus` operators into a single multi-input
`LogicalMinus`:
```text
LogicalMinus(all=[false])
t1
t2
t3
```
2. `MinusToAntiJoinRule`
Rewrites the multi-input `Minus` into a chain of anti joins with a top-level
distinct aggregate:
```text
LogicalAggregate(group=[{0}])
LogicalJoin(joinType=[anti])
LogicalJoin(joinType=[anti])
t1
t2
t3
```
3. `JoinPushExpressionsRule`
Extracts the `CAST` expressions from the join condition into projection
columns (`A0`), allowing the join to use direct column references:
text
LogicalProject(A=[$0])
LogicalJoin(condition=[=($1, $3)], joinType=[anti])
LogicalProject(A=[$0], A0=[CAST($0)])
LogicalProject(A=[$0], A0=[CAST($0)])
```
4. `EnumerableJoinRule`
Converts the logical anti joins into physical join implementations. The
inner anti join becomes a nested-loop join, while the outer anti join is
implemented as a hash join:
```text
EnumerableHashJoin(joinType=[anti])
EnumerableProject(A=[$0], A0=[CAST($0)])
EnumerableNestedLoopJoin(joinType=[anti])
...
```
5. `EnumerableAggregateRule`
Converts the top-level logical aggregate into a physical enumerable
aggregate:
```text
EnumerableAggregate(group=[{0}])
EnumerableHashJoin(joinType=[anti])
...
```
The final selected plan is:
```text
EnumerableAggregate
EnumerableHashJoin (anti)
EnumerableProject(A0=CAST(...))
EnumerableNestedLoopJoin (anti)
...
```
The original plan took this specific form because, within Volcano, every
rule generates a corresponding candidate RelNode. A particular scenario arises
with nested Minus operations: for each level of nesting, an equivalent
Aggregation-plus-Join structure is generated. Subsequently, during the final
cost-based selection phase, this specific structure was deemed to have the
lowest cost and was therefore selected. Please refer to the plan diagram below.
<img width="11864" height="4105" alt="graphviz"
src="https://github.com/user-attachments/assets/525d306a-9569-4e78-aece-28e1889fd201";
/>
This is my current understanding; please take another look to see if it is
clearly explained. @silundong @mihaibudiu
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