paul-rogers 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_r379850255
##########
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:
Just FYI: a clever thing Impala does is to use just plain SQL to gather
stats. Then, logic such as this is expressed in the SQL for the stats query. I
think Impala has a few functions specifically for stats gathering, such as NDV
estimates, etc.
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