after changing CAST() in group clause to CAST(CAST()), result unexpectedly become an empty set.

mysql> SELECT DISTINCT t2.c16 AS c16, CAST(t2.c14 AS FLOAT) AS col_1, STDDEV_POP(t2.c2) AS col_1_2 FROM t2 AS t2 CROSS JOIN t3 AS t3 ON (t3.c3 = t2.c1) GROUP BY t2.c16, CAST(t2.c14 AS FLOAT) HAVING NOT ST_COLLECT(77) IS NULL;

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

| c16                                                                                                                                                                      | col_1 | col_1_2 |

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

| {"k1": {"k2": 324, "k3": "user_33", "k4": {"k5": 24, "k6": "user12@example.com", "k7": {"k8": "city_39", "k9": "Sample Country"}}}, "k10": "2026-01-22T17:38:11.814999"} | 16.17 |  0.0000 |

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

1 row in set (0.00 sec)

mysql> SELECT DISTINCT t2.c16 AS c16, CAST(t2.c14 AS FLOAT) AS col_1, STDDEV_POP(t2.c2) AS col_1_2 FROM t2 AS t2 CROSS JOIN t3 AS t3 ON (t3.c3 = t2.c1) GROUP BY t2.c16, CAST(CAST(t2.c14 AS FLOAT) AS FLOAT) HAVING NOT ST_COLLECT(77) IS NULL;

Empty 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,

    c14 FLOAT(8,2) NULL,

    c16 JSON NULL,

    PRIMARY KEY (c1)

);

CREATE TABLE t3 (

    c3 INT NOT NULL

);

INSERT INTO t2 (c1, c2, c14, c16) VALUES (7923, 6081, 16.17, '{"k1": {"k2": 324, "k3": "user_33", "k4": {"k5": 24, "k6": "user12@example.com", "k7": {"k8": "city_39", "k9": "Sample Country"}}}, "k10": "2026-01-22T17:38:11.814999"}');

INSERT INTO t3 (c3) VALUES (7923);

SELECT DISTINCT t2.c16 AS c16, CAST(t2.c14 AS FLOAT) AS col_1, STDDEV_POP(t2.c2) AS col_1_2 FROM t2 AS t2 CROSS JOIN t3 AS t3 ON (t3.c3 = t2.c1) GROUP BY t2.c16, CAST(t2.c14 AS FLOAT) HAVING NOT ST_COLLECT(77) IS NULL;

SELECT DISTINCT t2.c16 AS c16, CAST(t2.c14 AS FLOAT) AS col_1, STDDEV_POP(t2.c2) AS col_1_2 FROM t2 AS t2 CROSS JOIN t3 AS t3 ON (t3.c3 = t2.c1) GROUP BY t2.c16, CAST(CAST(t2.c14 AS FLOAT) AS FLOAT) HAVING NOT ST_COLLECT(77) IS NULL;