beliefer commented on a change in pull request #27058: [SPARK-30395][SQL] When
one or more DISTINCT aggregate expressions operate on the same field, the
DISTINCT aggregate expression allows the use of the FILTER clause
URL: https://github.com/apache/spark/pull/27058#discussion_r364537516
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregates.scala
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@@ -118,6 +118,52 @@ import org.apache.spark.sql.types.IntegerType
* LocalTableScan [...]
* }}}
*
+ * Third example: single distinct aggregate function with filter clauses (in
sql):
+ * {{{
+ * SELECT
+ * COUNT(DISTINCT cat1) FILTER (WHERE id > 1) as cat1_cnt1,
+ * COUNT(DISTINCT cat1) as cat1_cnt2,
+ * SUM(value) AS total
+ * FROM
+ * data
+ * GROUP BY
+ * key
+ * }}}
+ *
+ * This translates to the following (pseudo) logical plan:
+ * {{{
+ * Aggregate(
+ * key = ['key]
+ * functions = [COUNT(DISTINCT 'cat1) with FILTER('id > 1),
+ * COUNT(DISTINCT 'cat1),
+ * sum('value)]
+ * output = ['key, 'cat1_cnt1, 'cat2_cnt2, 'total])
+ * LocalTableScan [...]
+ * }}}
+ *
+ * This rule rewrites this logical plan to the following (pseudo) logical plan:
+ * {{{
+ * Aggregate(
+ * key = ['key]
+ * functions = [count(if (('gid = 1)) 'phantom1 else null),
Review comment:
You can reference
https://github.com/apache/spark/blob/a4fd143fa92cb569764b669e5c53f6dfd1f1ae6a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregates.scala#L336
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