Estimates are low for a condition that satisfies all the rows of an INNODB table

--source include/have_sequence.inc

--source include/have_innodb.inc

CREATE TABLE t1 (id int PRIMARY KEY, a1 int, KEY (a1))engine=innodb;

INSERT INTO t1 SELECT seq FROM seq_1_to_50000;

MariaDB [test]> explain select * FROM t1 force index(a1) where a1=1;

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

| id   | select_type | table | type | possible_keys | key  | key_len | ref   | rows  | Extra       |

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

|    1 | SIMPLE      | t1    | ref  | a1            | a1   | 5       | const | 24485 | Using index |

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

MariaDB [test]> select count(*) from t1 where a1=1;

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

| count(*) |

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

|    50000 |

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