alamb commented on code in PR #7832:
URL: https://github.com/apache/arrow-datafusion/pull/7832#discussion_r1360892790
##########
datafusion/physical-plan/src/aggregates/mod.rs:
##########
@@ -1021,12 +1021,21 @@ impl ExecutionPlan for AggregateExec {
..Default::default()
}
}
- _ => Statistics {
- // the output row count is surely not larger than its input
row count
- num_rows: self.input.statistics().num_rows,
- is_exact: false,
- ..Default::default()
- },
+ _ => {
+ let input_stats = self.input.statistics();
+ // Input statistics is exact and number of rows not greater
than 1:
+ let is_exact = input_stats.is_exact
+ && (input_stats
+ .num_rows
+ .map(|num_rows| num_rows <= 1)
+ .unwrap_or(false));
+ Statistics {
+ // the output row count is surely not larger than its
input row count
Review Comment:
I don't know if it matters, but the output rows could be larger than the
input rows for `COUNT(*)` queries -- specifically if there are no input rows,
COUNT(*) still produces an output row 🤔
```
❯ create table t(x int) as values (1);
0 rows in set. Query took 0.001 seconds.
❯ select count(*) from t where x > 1000;
+----------+
| COUNT(*) |
+----------+
| 0 |
+----------+
```
##########
datafusion/physical-plan/src/aggregates/mod.rs:
##########
@@ -1021,12 +1021,21 @@ impl ExecutionPlan for AggregateExec {
..Default::default()
}
}
- _ => Statistics {
- // the output row count is surely not larger than its input
row count
- num_rows: self.input.statistics().num_rows,
- is_exact: false,
- ..Default::default()
- },
+ _ => {
+ let input_stats = self.input.statistics();
+ // Input statistics is exact and number of rows not greater
than 1:
+ let is_exact = input_stats.is_exact
+ && (input_stats
+ .num_rows
+ .map(|num_rows| num_rows <= 1)
+ .unwrap_or(false));
+ Statistics {
+ // the output row count is surely not larger than its
input row count
Review Comment:
I don't know if it matters, but the output rows could be larger than the
input rows for `COUNT(*)` queries -- specifically if there are no input rows,
COUNT(*) still produces an output row 🤔
```
❯ create table t(x int) as values (1);
0 rows in set. Query took 0.001 seconds.
❯ select count(*) from t where x > 1000;
+----------+
| COUNT(*) |
+----------+
| 0 |
+----------+
```
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