vvysotskyi commented on a change in pull request #1985: DRILL-7565: ANALYZE
TABLE ... REFRESH METADATA does not work for empty Parquet files
URL: https://github.com/apache/drill/pull/1985#discussion_r380128453
##########
File path:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/metadata/MetadataAggregateHelper.java
##########
@@ -313,8 +317,19 @@ private void addColumnAggregateCalls(FieldReference
fieldRef, String fieldName)
if (interestingColumns == null || interestingColumns.contains(fieldRef))
{
// collect statistics for all or only interesting columns if they are
specified
AnalyzeColumnUtils.COLUMN_STATISTICS_FUNCTIONS.forEach((statisticsKind,
sqlKind) -> {
+ // constructs "case when is not null projectMetadataColumn then
column1 else null end" call
+ // to avoid using default values for required columns when data for
empty result is obtained
Review comment:
Thanks for pointing this. Unfortunately, we can't use a plain SQL approach
to collect metadata, since we do not have information about the schema, so we
create aggregate calls dynamically. But Drill uses inbuilt aggregate functions
for collecting summary statistics (`MIN`, `MAX`, ...).
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