linrrzqqq opened a new pull request, #63605:
URL: https://github.com/apache/doris/pull/63605
Problem Summary:
Fix `VAR_SAMP`, `VARIANCE_SAMP`, and `STDDEV_SAMP` to return `NULL` when the
number of valid input values is less than or equal to 1.
Sample variance/stddev are undefined for `n <= 1`, so returning `0.0` is
misleading. `VAR_POP` / `STDDEV_POP` keep the existing behavior and still
return `0.0` for a single valid value.
before:
```sql
CREATE TABLE t (id INT, v DOUBLE) DUPLICATE KEY(id) DISTRIBUTED BY HASH(id)
BUCKETS 1 PROPERTIES('replication_num'='1');
INSERT INTO t VALUES (1, 5.0); -- 单行
SELECT VAR_SAMP(v), STDDEV_SAMP(v) FROM t;
+-------------+----------------+
| VAR_SAMP(v) | STDDEV_SAMP(v) |
+-------------+----------------+
| 0 | 0 |
+-------------+----------------+
```
now:
```sql
SELECT VAR_SAMP(v), STDDEV_SAMP(v) FROM t;
+-------------+----------------+
| VAR_SAMP(v) | STDDEV_SAMP(v) |
+-------------+----------------+
| NULL | NULL |
+-------------+----------------+
```
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