Dominik Labuda created CALCITE-4491:
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Summary: Aggregation of window function produces invalid SQL for
PostgreSQL
Key: CALCITE-4491
URL: https://issues.apache.org/jira/browse/CALCITE-4491
Project: Calcite
Issue Type: Bug
Components: core
Affects Versions: 1.26.0
Reporter: Dominik Labuda
h2. Issue
We tested the following behavior against PostgreSQL database, however more of
the supported dialects may be affected.
When aggregating the results of a window function an invalid SQL is generated.
I was able to replicate the behavior in tests with:
{code:java}
@Test void testAggregatingWindowFunction() {
final RelBuilder builder = relBuilder();
final RelNode root = builder
.scan("EMP")
.project(
builder.alias(
builder.getRexBuilder().makeOver(
builder.getTypeFactory().createSqlType(SqlTypeName.INTEGER),
SqlStdOperatorTable.RANK,
new ArrayList<>(),
new ArrayList<>(),
ImmutableList.of(new
RexFieldCollation(builder.field("SAL"), ImmutableSet.of())),
RexWindowBounds.UNBOUNDED_PRECEDING,
RexWindowBounds.UNBOUNDED_FOLLOWING,
true,
true,
false,
false,
false
),
"rank"
)
)
.as("tmp")
.aggregate(
builder.groupKey(),
builder.count(
true,
"cnt",
builder.field("tmp", "rank")
)
)
.build();
final String expectedSql = "SELECT COUNT(DISTINCT \"rank\") AS \"cnt\"\n" +
"FROM (SELECT RANK() OVER (ORDER BY \"SAL\") AS \"rank\"\n" +
"FROM \"scott\".\"EMP\") AS \"t\"";
assertThat(
toSql(root, PostgresqlSqlDialect.DEFAULT),
isLinux(expectedSql)
);
}
{code}
The code above fails, since it produces this SQL instead of the expected one,
which cannot be executed on PGSQL:
{noformat}
SELECT COUNT(DISTINCT RANK() OVER (ORDER BY "SAL")) AS "cnt"
FROM "scott"."EMP"
{noformat}
In that case I am getting this kinds of errors from DB:
{noformat}
ERROR: aggregate function calls cannot contain window function calls
{noformat}
h2. Suggested solution
Since _SqlDialect_ already contains support for determining whether the
databases support nested aggregations via _public boolean
supportsNestedAggregations()_ we could either add another method like _public
boolean supportsNestedWindows()_ or reuse the existing method for the window
purposes (which seems non-transparent). Then we will be able to handle the
behavior in _SqlImplementor.needNewSubQuery()_ similarly as it already does
with the aggregations.
Please let me know if you agree and I will be more than happy to provide you
with PR to review, thanks!
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