Steps to reproduce the issue

from
Downloads\Joomla_4.0.0-beta1-dev-Development-Full_Package.zip\installation\sql\mysqljoomla.sql and
Downloads\Joomla_4.0.0-beta1-dev-Development-Full_Package.zip\administrator\components\com_admin\sql\updates\mysql\4.0.0-2018-07-29.sql
execute this sql

DROP TABLE IF EXISTS xxx__finder_logging;

CREATE TABLE IF NOT EXISTS xxx__finder_logging (
searchterm VARCHAR(255) NOT NULL DEFAULT '',
md5sum VARCHAR(32) NOT NULL DEFAULT '',
query BLOB NOT NULL,
hits INT(11) NOT NULL DEFAULT 1,
results INT(11) NOT NULL DEFAULT 0,
PRIMARY KEY md5sum (md5sum),
INDEX searchterm (searchterm(191))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE=utf8mb4_general_ci;

Expected result

No warning

Actual result

Warning: #1280 Name 'md5sum' ignored for PRIMARY key.

System information (as much as possible)

Additional comments

change to
CREATE TABLE IF NOT EXISTS #__finder_logging (
searchterm VARCHAR(255) NOT NULL DEFAULT '',
md5sum VARCHAR(32) NOT NULL DEFAULT '',
query BLOB NOT NULL,
hits INT(11) NOT NULL DEFAULT 1,
results INT(11) NOT NULL DEFAULT 0,
PRIMARY KEY (md5sum),
INDEX searchterm (searchterm(191))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE=utf8mb4_general_ci;