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Fix global empty aggregation pushdown in JDBC connectors #12603
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Test aggregation over UNION ALL of aggregation
Fix global empty aggregation pushdown in JDBC connectors
May 31, 2022
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plugin/trino-base-jdbc/src/main/java/io/trino/plugin/jdbc/DefaultQueryBuilder.java
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@wendigo thanks for your quick review. PTAL, i changed the approach. |
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core/trino-main/src/test/java/io/trino/sql/query/QueryAssertions.java
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In a query like `...FROM (SELECT count(*) FROM t)` the aggregation is global, yet the aggregation itself may be unused and pruned away. In such case, JDBC connectors `ConnectorMetadata.applyAggregation` would produce a query with no aggregation function (as it was pruned away) and with no `GROUP BY`, since global aggregation was supposed to be implicit, so returning original table, without aggregating. This commit fixes this by avoiding such pushdown on the engine side. In such case, the engine knows the result without involving the connector. Additionally, a safety check is added in `DefaultJdbcMetadata`.
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@@ -138,6 +139,11 @@ public static Optional<PlanNode> pushAggregationIntoTableScan( | |||
LiteralEncoder literalEncoder = new LiteralEncoder(plannerContext); | |||
Session session = context.getSession(); | |||
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if (groupingKeys.isEmpty() && aggregations.isEmpty()) { | |||
// Global aggregation with no aggregation functions | |||
return Optional.of(new ValuesNode(aggregationNode.getId(), 1)); |
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This will be further generalized in #12612
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In a query like
...FROM (SELECT count(*) FROM t)
the aggregation isglobal, yet the aggregation itself may be unused and pruned away.
In such case, JDBC connectors
ConnectorMetadata.applyAggregation
wouldproduce a query with no aggregation function (as it was pruned away) and
with no
GROUP BY
, since global aggregation was supposed to beimplicit, so returning original table, without aggregating.
This commit fixes this by avoiding such pushdown on the engine side. In
such case, the engine knows the result without involving the connector.
Additionally, a safety check is added in
DefaultJdbcMetadata
.Fixes #12598