MDEV-39194 SUM(b'1100') and SUM(DISTINCT b'1100') return different numeric results for the same BIT literal (e.g. 12 vs 9)

[DerZc]

SUM(DISTINCT b'1100') can produce a different numeric value from SUM(b'1100'), despite both aggregating the same bit literal. The DISTINCT expression should return 12.

Bug report: https://jira.mariadb.org/browse/MDEV-39194

Root cause

The DISTINCT temporary field is chosen from the argument's type handler and metadata. That can materialize a bit literal in a representation that disagrees with the aggregate's numeric conversion and subsequent value consumption.

Changes

• Choose the DISTINCT numeric temporary field using the aggregate's type handler and metadata.
• Retain the existing temporary-table and Unique-based deduplication path.

Regression coverage

The regression evaluates SUM(DISTINCT b'1100') and checks the numeric result 12.

• mysql-test/main/sum_distinct_bit_literal.result
• mysql-test/main/sum_distinct_bit_literal.test

Validation

On 11.4 at d10e5d726799b1cd57cc866f40aad68c720803da:

• The server build passed.
• main.sum_distinct_bit_literal failed on the unchanged target branch and passed with this fix.
• Existing MTR tests passed: main.func_group, main.group_by, main.select, main.type_bit, main.type_bit_innodb, main.type_decimal, main.type_float.
• MTR reported no test-state cleanup failures.
• The full regression suite was not run.

[CLAassistant]

All committers have signed the CLA.