after changing STD(x) to STD(-x), the value unexpectedly become different

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OceanBase version

5.7.25 OceanBase_CE 4.3.5.4

Self Hosted

Self Hosted (Docker)

Environment

Linux LAPTOP-2SQAVLB0 6.6.87.2-microsoft-standard-WSL2 #1 SMP PREEMPT_DYNAMIC Thu Jun 5 18:30:46 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Steps to reproduce

DROP DATABASE IF EXISTS test;
CREATE DATABASE IF NOT EXISTS test;
SET GLOBAL sort_buffer_size = 64 * 1024 * 1024;
SET GLOBAL read_rnd_buffer_size = 8 * 1024 * 1024;
USE test;

CREATE TABLE t2 (
    c13 DATETIME NULL
);

INSERT INTO t2 (c13) VALUES ('2026-01-06 13:03:11');
WITH cte_670 AS (SELECT MAX(ADDDATE(bin51.c13, 'DAY')) AS col_2 FROM t2 AS bin51) SELECT cte.col_2 AS col_2, STD(cte.col_2) AS col_1_2 FROM cte_670 AS cte GROUP BY cte.col_2;
WITH cte_670 AS (SELECT MAX(ADDDATE(bin51.c13, 'DAY')) AS col_2 FROM t2 AS bin51) SELECT cte.col_2 AS col_2, STD(-cte.col_2) AS col_1_2 FROM cte_670 AS cte GROUP BY cte.col_2;

✔️ Expected Behavior

col_1_2's value should be 0
Aditionally,In mysql 8.0.20,the value is the same

mysql> WITH cte_670 AS (SELECT MAX(ADDDATE(bin51.c13, 'DAY')) AS col_2 FROM t2 AS bin51) SELECT cte.col_2 AS col_2, STD(cte.col_2) AS col_1_2 FROM cte_670 AS cte GROUP BY cte.col_2;
+---------------------+---------+
| col_2               | col_1_2 |
+---------------------+---------+
| 2026-01-06 13:03:11 |       0 |
+---------------------+---------+
1 row in set, 1 warning (0.00 sec)

mysql> WITH cte_670 AS (SELECT MAX(ADDDATE(bin51.c13, 'DAY')) AS col_2 FROM t2 AS bin51) SELECT cte.col_2 AS col_2, STD(-cte.col_2) AS col_1_2 FROM cte_670 AS cte GROUP BY cte.col_2;
+---------------------+---------+
| col_2               | col_1_2 |
+---------------------+---------+
| 2026-01-06 13:03:11 |       0 |
+---------------------+---------+
1 row in set, 1 warning (0.00 sec)

In oceanbase:

mysql> WITH cte_670 AS (SELECT MAX(ADDDATE(bin51.c13, 'DAY')) AS col_2 FROM t2 AS bin51) SELECT cte.col_2 AS col_2, STD(cte.col_2) AS col_1_2 FROM cte_670 AS cte GROUP BY cte.col_2;
+---------------------+---------+
| col_2               | col_1_2 |
+---------------------+---------+
| 2026-01-06 13:03:11 |       0 |
+---------------------+---------+
1 row in set (0.00 sec)

mysql> WITH cte_670 AS (SELECT MAX(ADDDATE(bin51.c13, 'DAY')) AS col_2 FROM t2 AS bin51) SELECT cte.col_2 AS col_2, STD(-cte.col_2) AS col_1_2 FROM cte_670 AS cte GROUP BY cte.col_2;
+---------------------+--------------------+
| col_2               | col_1_2            |
+---------------------+--------------------+
| 2026-01-06 13:03:11 | 192579.96593363496 |
+---------------------+--------------------+
1 row in set (0.00 sec)

❌ Actual Behavior

mysql> WITH cte_670 AS (SELECT MAX(ADDDATE(bin51.c13, 'DAY')) AS col_2 FROM t2 AS bin51) SELECT cte.col_2 AS col_2, STD(cte.col_2) AS col_1_2 FROM cte_670 AS cte GROUP BY cte.col_2;
+---------------------+---------+
| col_2               | col_1_2 |
+---------------------+---------+
| 2026-01-06 13:03:11 |       0 |
+---------------------+---------+
1 row in set (0.00 sec)

mysql> WITH cte_670 AS (SELECT MAX(ADDDATE(bin51.c13, 'DAY')) AS col_2 FROM t2 AS bin51) SELECT cte.col_2 AS col_2, STD(-cte.col_2) AS col_1_2 FROM cte_670 AS cte GROUP BY cte.col_2;
+---------------------+--------------------+
| col_2               | col_1_2            |
+---------------------+--------------------+
| 2026-01-06 13:03:11 | 192579.96593363496 |
+---------------------+--------------------+
1 row in set (0.00 sec)

Start by running the provided OceanBase SQL reproduction and trace the STD aggregate with a DATETIME expression after unary negation. Compare the type conversion and aggregate input for STD(cte.col_2) and STD(-cte.col_2); done when both forms return 0, consistent with the expected MySQL behavior.