kgyrtkirk commented on code in PR #17550:
URL: https://github.com/apache/druid/pull/17550#discussion_r1905623884
##########
extensions-core/multi-stage-query/src/test/java/org/apache/druid/msq/exec/MSQSelectTest.java:
##########
@@ -2494,12 +2494,11 @@ public void testJoinUsesDifferentAlgorithm(String
contextName, Map<String, Objec
new QueryDataSource(
newScanQueryBuilder()
.dataSource("foo")
- .virtualColumns(expressionVirtualColumn("v0", "0",
ColumnType.LONG))
- .columns("v0")
+ .columns("__time")
.columnTypes(ColumnType.LONG)
.context(defaultScanQueryContext(
queryContext,
- RowSignature.builder().add("v0",
ColumnType.LONG).build()
+ RowSignature.builder().add("__time",
ColumnType.LONG).build()
Review Comment:
no columns are needed from the left hand side; but Calcite has some tweaks
here and there to avoid relnodes with `0` columns.
This PR suppresses the introduction of a column with the `0` value by the
[Fieldtrimmer](https://github.com/apache/calcite/blob/7d4135eb17e2a70ac608ab1dd3e5a7f4d03706da/core/src/main/java/org/apache/calcite/sql2rel/RelFieldTrimmer.java#L575-L602)
but in one of the rules there is also an unconditional projection of the
[1st
columns](https://github.com/apache/calcite/blob/7d4135eb17e2a70ac608ab1dd3e5a7f4d03706da/core/src/main/java/org/apache/calcite/rel/rules/PushProjector.java#L458-L464)
which causes this change.
We should be able to handle the case of empty columns - I wanted to dig into
that more deeply ; as it seems like there are also some rule combinations which
may lead to an empty column set...(but forgot the testcase)
I think that in general Calcite should be able to handle these things - and
we should only make
corrections in the execution engine if it causes issues.
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