MariaDB [test]> show create table t20\G
*************************** 1. row ***************************
       Table: t20
Create Table: CREATE TABLE `t20` (
  `pk` int(11) NOT NULL,
  `a` int(11) DEFAULT NULL,
  `b` int(11) DEFAULT NULL,
  `c` int(11) DEFAULT NULL,
  PRIMARY KEY (`pk`),
  KEY `a` (`a`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1


MariaDB [test]> set @a=0;
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> truncate table t20;
Query OK, 0 rows affected (0.26 sec)

MariaDB [test]> insert into t20 select @a:=@a+1, @a/100, @a/100, @a/100 from seq_1_to_1000;
Query OK, 1000 rows affected (0.36 sec)
Records: 1000  Duplicates: 0  Warnings: 0

MariaDB [test]> select count(*) from t20;
+----------+
| count(*) |
+----------+
|     1000 |
+----------+
1 row in set (0.01 sec)

MariaDB [test]> select count(*) from t20 where a=2;
+----------+
| count(*) |
+----------+
|      100 |
+----------+
1 row in set (0.00 sec)

MariaDB [test]> explain delete from t20 where a=2;
+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
| id   | select_type | table | type  | possible_keys | key  | key_len | ref  | rows | Extra       |
+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
|    1 | SIMPLE      | t20   | range | a             | a    | 5       | NULL |  100 | Using where |
+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
1 row in set (0.00 sec)