Equivalent view extraction retags `UNION ALL` constant `1` as a `BIT(1)` byte

Under semantic-equivalent rewriting, the source and mutated queries are logically equivalent, but produce different results in polardbx-sql.
Summary: when an empty first UNION ALL arm has type BIT(1), moving the second arm into a view changes integer constant 1 into byte string 0x01.

version: 5.4.19-SNAPSHOT

How to repeat:

DROP DATABASE IF EXISTS t1;
CREATE DATABASE t1;
USE t1;

CREATE TABLE t2 (
  c12 BIT(1)
);

-- Source Original SQL
SELECT c12 AS col1 FROM t2 WHERE 1=0
UNION ALL
SELECT 1 AS col1;

-- View SQL
CREATE VIEW V AS
SELECT 1 AS col1;

-- Mutated SQL
SELECT c12 AS col1 FROM t2 WHERE 1=0
UNION ALL
SELECT col1 FROM V;

Observed result - Query A (original):

Observed result - Query B (mutated):

Start by running the supplied polardbx-sql reproduction with the original UNION ALL query and the view-based query, then trace the semantic-equivalent rewriting and type handling for the empty BIT(1) arm. Done means both queries return integer 1 rather than converting the view result to the byte string 0x01.