xuzifu666 commented on code in PR #5019:
URL: https://github.com/apache/calcite/pull/5019#discussion_r3425163533
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core/src/main/java/org/apache/calcite/adapter/enumerable/RexImpTable.java:
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@@ -1250,6 +1251,7 @@ void populate2() {
NotJsonImplementor.of(
new MethodImplementor(BuiltInMethod.IS_JSON_SCALAR.method,
NullPolicy.NONE, false)));
+ define(FILTER, new FilterImplementor());
Review Comment:
The FILTER operator implements conditional aggregation in SQL, such as:
``` SUM(salary) FILTER (WHERE department = 'Sales') COUNT(*) FILTER (WHERE
age > 30)```
Processing Pipeline:
1. SQL Parsing → ```FILTER (WHERE condition)``` parsed as
```SqlKind.FILTER``` node
2. Validation → Checks aggregate-FILTER compatibility (we reject
```COUNT(DISTINCT) + FILTER``` in window functions)
3. SQL-to-Relational Conversion → FILTER condition extracted and stored
4. Code Generation → Registers FilterImplementor to translate FILTER into
executable code
I had added a comment about it.
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