github-actions[bot] commented on code in PR #65548:
URL: https://github.com/apache/doris/pull/65548#discussion_r3576573151
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be/src/format_v2/table_reader.h:
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@@ -1433,16 +1433,15 @@ class TableReader {
request->columns.clear();
if (agg_type == TPushAggOp::type::COUNT) {
// COUNT pushdown historically meant COUNT(*) and therefore
carried no columns. For
- // complex COUNT(col), materializing the full MAP/LIST/STRUCT
value only to test the
- // top-level NULL bit can be extremely expensive. When the scan
projects exactly one
- // directly-mapped complex column, pass that file column to the
reader so formats such
- // as Parquet can count the column shape from metadata/levels
without decoding payload
- // values like MAP value strings. Other COUNT cases stay on the
existing row-count path
- // to avoid changing count(*) semantics.
+ // COUNT(col), Nereids retains exactly the counted slot in the
file scan. Pass that
+ // single direct mapping for both scalar and complex columns:
besides allowing nullable
+ // complex values to be counted from levels, it lets the file
reader validate logical
+ // types before returning footer row counts. For example, a
required TIME_MILLIS leaf
+ // has the same count as COUNT(*), but it must still fail as an
unsupported requested
+ // column rather than silently returning the row-group count.
if (_data_reader.column_mapper->mappings().size() == 1) {
const auto& mapping =
_data_reader.column_mapper->mappings()[0];
if (mapping.file_local_id.has_value() && mapping.file_type !=
nullptr &&
-
is_complex_type(remove_nullable(mapping.file_type)->get_primitive_type()) &&
Review Comment:
This still needs to preserve the COUNT(*) vs COUNT(col) distinction.
`TPushAggOp::COUNT` is used for both shapes, and the only signal here is the
post-pruning scan mapping. For a real `COUNT(*)`, column pruning can leave one
arbitrary physical column under the scan (`pruneOutput()` picks a minimum
column, then `newProjectIfNotPruned()` wraps it with a literal/empty project),
so this branch turns an empty row-count request into `COUNT(that_column)`. File
readers such as Parquet/ORC then count only non-null values for a nullable
placeholder column, or reject an unsupported placeholder leaf, even though
COUNT(*) should return the selected row count without observing any column
nullability/logical type. Please pass a count column only when FE/BE knows the
aggregate argument was `COUNT(col)` and the mapping is semantically countable;
true COUNT(*) requests should keep `request.columns` empty.
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