[MDEV-23435] Functions do not convert numbers to character_set_results - Jira

Fields of the numeric and temporal data types convert to character_set_results, while functions do not:

This is bad when character_set_results is set to character sets like UCS2, UTF16, UTF32, as well as filename.

SET character_set_results=filename;

CREATE OR REPLACE TABLE t1 (a DATETIME(6));

INSERT INTO t1 VALUES ('2001-01-01 00:00:00.000000');

SELECT a, COALESCE(a) AS c FROM t1;

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

| a                                                  | c                          |

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

| 2001@002d01@002d01@002000@003a00@003a00@002e000000 | 2001-01-01 00:00:00.000000 |

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

Notice, the field converted its value to 'filename', while the function did not.

The same problem is repeatable with INT (and also with TINYINT, SHORTINT, MEDIUMINT, BIGINT):

SET character_set_results=filename;

CREATE OR REPLACE TABLE t1 (a INT);

INSERT INTO t1 VALUES (-3);

SELECT a, COALESCE(a) AS c FROM t1;

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

| a      | c    |

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

| @002d3 |   -3 |

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

relates to

MDEV-23162 Improve Protocol performance for numeric data

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