Range optimizer's const-bound folding mishandles numeric-overflow string literals (e.g. `'-1e500'`) on a prefix(1) index, producing "Impossible WHERE" and returning 0 rows where 12 are correct.

DROP DATABASE IF EXISTS bug_prefix_overflow;

CREATE DATABASE bug_prefix_overflow;

USE bug_prefix_overflow;

CREATE TABLE t0(c0 MEDIUMTEXT);

INSERT INTO t0(c0) VALUES ('0.5'),('123'),('abc'),('-2117222092'),('hello'),('Cv');

INSERT INTO t0(c0) VALUES ('*#'),('!b'),('0I'),('1*tE'),('4Ti}k'),('5(2*07');

INSERT INTO t0(c0) VALUES ('wp'),('x&'),('jx+');

CREATE INDEX prefix_idx ON t0(c0(1));

ANALYZE TABLE t0;

-- Ground truth (string compare, no index): 12

SELECT SUM(CASE WHEN c0 >= '-1e500' AND c0 <= '᪾JwQ [' THEN 1 ELSE 0 END) AS truth FROM t0;

-- BUG: returns 0

SELECT COUNT(*) FROM t0 WHERE c0 >= '-1e500' AND c0 <= '᪾JwQ [';

-- Correct: returns 12

SELECT COUNT(*) FROM t0 IGNORE INDEX(prefix_idx) WHERE c0 >= '-1e500' AND c0 <= '᪾JwQ [';

-- Diagnostic: prefix(2) is fine, prefix(3) is fine — only prefix(1) breaks.

DROP INDEX prefix_idx ON t0;

CREATE INDEX prefix_idx2 ON t0(c0(2));

ANALYZE TABLE t0;

SELECT COUNT(*) FROM t0 FORCE INDEX(prefix_idx2) WHERE c0 >= '-1e500' AND c0 <= '᪾JwQ [';

-- 12, correct

SHOW CREATE TABLE t0:

  CREATE TABLE `t0` (

    `c0` mediumtext DEFAULT NULL,

    KEY `prefix_idx` (`c0`(1))

  ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci

ground truth (CASE WHEN)        : 12

default plan (uses prefix(1))   : 0   <-- WRONG

EXPLAIN default                 : Impossible WHERE noticed after reading const tables

IGNORE INDEX(prefix_idx)        : 12

EXPLAIN IGNORE INDEX            : type=ALL, rows=15

prefix_idx2 (length 2) FORCE    : 12  <-- correct