FLOAT ZEROFILL column renders negative zero as `0000000000-0` (sign character at wrong position)

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OceanBase version

5.7.25-OceanBase_CE-v4.5.0.0

Self Hosted

Self Hosted (OBD)

Environment

obclient(root@sys)[oceanbase]> select version();
+------------------------------+
| version()                    |
+------------------------------+
| 5.7.25-OceanBase_CE-v4.5.0.0 |
+------------------------------+
1 row in set (0.002 sec)

obclient(root@sys)[oceanbase]> SHOW VARIABLES LIKE 'version_comment';
+-----------------+------------------------------------------------------------------------------------------------------------------+
| Variable_name   | Value                                                                                                            |
+-----------------+------------------------------------------------------------------------------------------------------------------+
| version_comment | OceanBase_CE 4.5.0.0 (r100000012025112711-0e8d5ad012baf0953b2032a35a88bdf8886e9a7a) (Built Nov 27 2025 12:06:16) |
+-----------------+------------------------------------------------------------------------------------------------------------------+
1 row in set (0.015 sec)
---

Steps to reproduce

-- Step 1: Create a FLOAT ZEROFILL table
DROP TABLE IF EXISTS ob_bug_float_zerofill_mre;
CREATE TABLE ob_bug_float_zerofill_mre (c0 FLOAT ZEROFILL NULL);

-- Step 2: Insert a negative-zero value via string coercion
-- ('-0' is a valid MySQL input; no error or warning is raised on either MySQL or OceanBase)
INSERT INTO ob_bug_float_zerofill_mre (c0) VALUES ('-0');

-- Step 3: Query the stored value with HEX diagnostic
SELECT
    c0,
    HEX(CAST(c0 AS CHAR)) AS c0_hex
FROM ob_bug_float_zerofill_mre;

✔️ Expected Behavior

The value should be displayed as a valid zero-padded string.
Acceptable outputs are either:

• 000000000000 — the negative zero is normalised to positive zero before formatting, or
• -00000000000 — the sign character is placed at the beginning of the padded string.

❌ Actual Behavior

OceanBase renders the value as 0000000000-0, with the sign character - placed
at position 10 (the end of the string) instead of position 0 (the beginning).
No error or warning is raised.

+--------------+--------------------------+
| c0           | c0_hex                   |
+--------------+--------------------------+
| 0000000000-0 | 303030303030303030302D30 |
+--------------+--------------------------+
1 row in set (0.007 sec)

HEX breakdown:

Byte position:  0    1    2    3    4    5    6    7    8    9    10
Hex value:      30   30   30   30   30   30   30   30   30   2D   30
Decoded:        0    0    0    0    0    0    0    0    0    -    0
                                                             ^
                                              0x2D ('-') is here — should be at position 0

Start by running the provided SQL reproduction for FLOAT ZEROFILL and inspect the formatting entry point that produces the displayed value. Trace how the negative-zero sign and zero padding are ordered, then verify that the output is normalized or has its sign at the beginning without errors or warnings.