after changing MONTH(hue12.c5) in group by clause, col_2's value unexpectedly change to '0000-00-00'

mysql> (SELECT DISTINCT (SELECT BIT_XOR(83) AS subq_col) AS col_1, TIME(hue12.c5) AS col_2, MONTH(hue12.c5) AS col_3, ST_COLLECT(hue12.c11) AS col_4, hue12.c15 AS c15 FROM t3 AS hue12 GROUP BY hue12.c15, TIME(hue12.c5), hue12.c15, MONTH(hue12.c5 + INTERVAL '12' MONTH), hue12.c15, hue12.c15, hue12.c15, MONTH(hue12.c5) ORDER BY hue12.c15 DESC) UNION SELECT 37 AS col_1, irk20.c5 AS col_2, irk20.c14 AS col_3, irk20.c8 AS col_4, irk20.c15 AS col_5 FROM t2 AS irk20;

+-------+---------------------+-------+------------------------------------------------------------------------+--------+

| col_1 | col_2               | col_3 | col_4                                                                  | c15    |

+-------+---------------------+-------+------------------------------------------------------------------------+--------+

|    83 | 2026-01-25 00:33:04 | 10.00 | 0x000000000104000000010000000101000000E50E9BC8CCD51CC011514CDE00C35BC0 |   NULL |

|    37 | 2025-06-14 00:00:00 | 76.40 | 0x2EE6AA8B771A30                                                       | 8.9900 |

+-------+---------------------+-------+------------------------------------------------------------------------+--------+

2 rows in set (0.00 sec)

mysql> (SELECT DISTINCT (SELECT BIT_XOR(83) AS subq_col) AS col_1, TIME(hue12.c5) AS col_2, MONTH(hue12.c5) AS col_3, ST_COLLECT(hue12.c11) AS col_4, hue12.c15 AS c15 FROM t3 AS hue12 GROUP BY hue12.c15, TIME(hue12.c5), hue12.c15, MONTH(hue12.c5), hue12.c15, hue12.c15, hue12.c15 ORDER BY hue12.c15 DESC) UNION SELECT 37 AS col_1, irk20.c5 AS col_2, irk20.c14 AS col_3, irk20.c8 AS col_4, irk20.c15 AS col_5 FROM t2 AS irk20;

+-------+---------------------+-------+------------------------------------------------------------------------+--------+

| col_1 | col_2               | col_3 | col_4                                                                  | c15    |

+-------+---------------------+-------+------------------------------------------------------------------------+--------+

|    83 | 0000-00-00 00:00:00 | 10.00 | 0x000000000104000000010000000101000000E50E9BC8CCD51CC011514CDE00C35BC0 |   NULL |

|    37 | 2025-06-14 00:00:00 | 76.40 | 0x2EE6AA8B771A30                                                       | 8.9900 |

+-------+---------------------+-------+------------------------------------------------------------------------+--------+

2 rows in set (0.00 sec)

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 (

    c1 INT NOT NULL AUTO_INCREMENT,

    c2 INT NOT NULL,

    c3 DECIMAL(10,2) NOT NULL,

    c4 VARCHAR(50) NOT NULL,

    c5 DATE NOT NULL,

    c6 MEDIUMTEXT NULL,

    c7 LONGTEXT NULL,

    c8 MEDIUMBLOB NULL,

    c9 LONGBLOB NULL,

    c10 ENUM('value1','value2','value3') NULL,

    c11 SET('a','b','c','d') NULL,

    c12 BIT(8) NULL,

    c13 DATETIME NULL,

    c14 FLOAT(8,2) NULL,

    c15 DOUBLE(12,4) NULL,

    c16 JSON NULL,

    PRIMARY KEY (c1)

);

CREATE TABLE t3 (

    c1 INT NOT NULL AUTO_INCREMENT,

    c2 INT NOT NULL,

    c3 INT NOT NULL,

    c4 YEAR NOT NULL,

    c5 DATETIME NULL,

    c6 TINYINT NULL,

    c7 SMALLINT NULL,

    c8 MEDIUMINT NULL,

    c9 BIGINT NULL,

    c10 LONGTEXT NULL,

    c11 GEOMETRY NULL,

    c12 TINYTEXT NULL,

    c13 TINYBLOB NULL,

    c14 SET('x','y','z') NULL,

    c15 TINYINT(1) NULL,

    PRIMARY KEY (c1)

);

INSERT INTO t2 (c1, c2, c3, c4, c5, c6, c7, c8, c9, c10, c11, c12, c13, c14, c15, c16) VALUES (5217, 498, 835.13, 'sample_fNfG', '2025-06-14', 'sample_fmk5nNJEcTlHvPeK898aRIeFPiKwTlhiLdzE', 'sample_fzqAtYYMglBoJysRqpTHHQJENLTDVHZ0IJ0dYYGsUKN2pQyWIwU0tpiGSGsH9A4e92oqZVLOBW9bWR5gOyaNt94WADineBTnCRmhWToq8EmCIhArS71v7BaW1zI4lsfklEaqKvqIUtPFtugfhTKoiM5WBcIKOUzQcT1b2E1Wu0Lv6NxhQgiTywCSiyq0JOr7EFd6HsqXkd40Z8AWnaZJc9bilZiskcjeU9cSMoK0nHJrlHt7CSSTShP4oBFVBPBoT0VwfSdP8RLptWZBaikg12SCcGdoy8IPtlZO0FSbCmhbZoKkA4CcQt7Q0N4Ka50cdVIkk9GJ1Pm96HQj0FR81ya1StN6lJFMD41K0uyoQ2zyffdYQgPg28Ymn8tXCa8tT2OqOBkYGRsuEeJMCFFTl1RJ7CwaOLodqC4JZAWSgQBJGV3Kxszhds2UA1Tpk7XBvQfuTyH6tXPcOzXlEfgB1dsf5gHCivSlgfpFqDFuJXvDI09GUSszpoXY82L0yolScDsPT5LK7RvcU4EKWm3W5M5gXZyXn9rv6SewdyunnxH4VLWAFTNe0jCwNpLcjALBzJm1JiDTDSF9L4ZxhyQ8DMBugZ2b5OME5XS9gRdDuys3UMwbf5sopOULafb6osANgMlHedPl0JfR3mHjrCV04ODGuS0wRh2MvsE9XhwcOBK1boL8TvqylgwUapO0G3DmwJeTbGfcxjhwVLeeJhj76Ef4KoXEUE44pcG8EpjgWG02uE6mjKkjEJChNK7Zd5nb3eucXRIqD2vAvlibTUQ4nwUsJFgOjFU7YUCIQwqDX39rErIOxrWfsY6kBHOlYDjBUNAQ8euVN8fpmjtnn279AgOHT24iE63umZciHBknqLlghhqEYPNuHli46mTqtEQ6FiDLtcVu0uRRPN21cW5DrwROObjixx4P4He8CAbp9NJ3iv2RSeAYuHzJAbmvyakOkTTipmEnhQZzmZ3j8OhX26vZR0pJ6B7fTGI5KDSv9SzGJr1fpeRnnPsf2Y1cwSBeVHUg47tYPstnFsl0fdiRrQOPVugF5JQ2QpKVwAN3ysYINlSe6DVsFIMb6ohNYPZIT8Wu5s0J3NLUTsYkZJVd05lmO8ATSfiwS3tW2NIr2GpG1asTXFfsvUzU', X'2EE6AA8B771A30', X'E889B1C38468C291', 'value2', 'd,c,b,a', b'10100010', '2025-03-09 17:59:43', 76.40, 8.99, '{"k1": 758, "k2": "mixed_41", "k3": ["tag_83"], "k4": {"k5": "B", "k6": [87, 5], "k7": {"k8": "user_61", "k9": "2026-01-22T17:38:11.813764"}}, "k10": true}');

INSERT INTO t3 (c1, c2, c3, c4, c5, c6, c7, c8, c9, c10, c11, c12, c13, c14, c15) VALUES (9473, 3166, 7923, 2009, '2025-10-28 00:33:04', 64, 33, 23, 5, 'sample_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', ST_GeomFromText('POINT(-7.208789 -111.046928)'), 'sample_lo1SDGmMjznqDAbPH7lv1PLIycmmGnug3w9c1EMVaOOvVY0FM7GLWSZHVE6MVSrkzdR1XlrSer0Ae6U0ldCAgDDUG', X'CBBA34E99F8CDA95E4A2AFDF8210', 'z', NULL);

(SELECT DISTINCT (SELECT BIT_XOR(83) AS subq_col) AS col_1, TIME(hue12.c5) AS col_2, MONTH(hue12.c5) AS col_3, ST_COLLECT(hue12.c11) AS col_4, hue12.c15 AS c15 FROM t3 AS hue12 GROUP BY hue12.c15, TIME(hue12.c5), hue12.c15, MONTH(hue12.c5), hue12.c15, hue12.c15, hue12.c15 ORDER BY hue12.c15 DESC) UNION SELECT 37 AS col_1, irk20.c5 AS col_2, irk20.c14 AS col_3, irk20.c8 AS col_4, irk20.c15 AS col_5 FROM t2 AS irk20;

(SELECT DISTINCT (SELECT BIT_XOR(83) AS subq_col) AS col_1, TIME(hue12.c5) AS col_2, MONTH(hue12.c5) AS col_3, ST_COLLECT(hue12.c11) AS col_4, hue12.c15 AS c15 FROM t3 AS hue12 GROUP BY hue12.c15, TIME(hue12.c5), hue12.c15, MONTH(hue12.c5 + INTERVAL '12' MONTH), hue12.c15, hue12.c15, hue12.c15, MONTH(hue12.c5) ORDER BY hue12.c15 DESC) UNION SELECT 37 AS col_1, irk20.c5 AS col_2, irk20.c14 AS col_3, irk20.c8 AS col_4, irk20.c15 AS col_5 FROM t2 AS irk20;

mysql> select @@version;

+------------------------+

| @@version              |

+------------------------+

| 12.1.2-MariaDB-ubu2404 |

+------------------------+

1 row in set (0.00 sec)