我有一个查询需要一天多的时间才能完成，在temp\u message\u split表中有1700128条记录，所以请帮助我解释这个问题
下面提供了create table语句和explain plan。

UPDATE TEMP_MESSAGE_SPLIT t1 , TEMP_MESSAGE_SPLIT t2
    SET t1.STATUS = 'D'
    WHERE
    (t1.temp_message_split_key < t2.temp_message_split_key AND t1.DH_MEMBER_ID = t2.DH_MEMBER_ID)
    AND  nullif(t1.dh_member_id,'') IS NOT NULL;

下面是创建表ddl

CREATE TABLE
temp_message_split
(
    FIRST_NAME VARCHAR(20),
    LAST_NAME VARCHAR(30),
    DOB VARCHAR(10),
    EMPLOYEE_ID VARCHAR(20),
    CES_CUST_NUM VARCHAR(7),
    MED_POLICY_NUM VARCHAR(20),
    EMAIL_ADDR VARCHAR(50),
    DH_MEMBER_ID VARCHAR(9),
    ALT_ID VARCHAR(20),
    DRSN VARCHAR(2),
    SSN VARCHAR(9),
    EPIPHANY_MEMBER_ID VARCHAR(18),
    PORTAL_ADDRESS VARCHAR(30),
    STATEMENT_VENDOR VARCHAR(20),
    CONTENT_KEY VARCHAR(18),
    EPIPHANY_COMMUNICATION_ID VARCHAR(200),
    PRIORITY VARCHAR(4),
    DAYS_UNTIL_EXPIRED VARCHAR(4),
    CONTENT_DTL_KEY VARCHAR(18),
    STATUS VARCHAR(1),
    ACTIVATION_MEMBER_KEY bigint,
    MESSAGE_BOARD_KEY bigint,
    PORTAL_STATEMENT_LOC_KEY bigint,
    temp_message_split_KEY bigint NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (temp_message_split_KEY),
    INDEX EPIPHANY_COMMUNICATION_ID_IDX (EPIPHANY_COMMUNICATION_ID),
    INDEX TEMP_MESSAGE_SPLIT_IDX2 (ALT_ID),
    INDEX TEMP_MESSAGE_SPLIT_IDX3 (DRSN),
    INDEX TEMP_MESSAGE_SPLIT_IDX4 (ALT_ID, DRSN),
    INDEX TEMP_MESSAGE_SPLIT_IDX1 (DH_MEMBER_ID)
)
ENGINE=InnoDB DEFAULT CHARSET=utf8;

下面是它的解释计划：

+----+-------------+-------+------------+-------+---------------------------------+-------------------------+---------+------+---------+----------+------------------------------------------------+
| id | select_type | table | partitions | type  | possible_keys                   | key                     | key_len | ref  | rows    | filtered | Extra                                          |
+----+-------------+-------+------------+-------+---------------------------------+-------------------------+---------+------+---------+----------+------------------------------------------------+
|  1 | SIMPLE      | t2    | NULL       | index | PRIMARY,TEMP_MESSAGE_SPLIT_IDX1 | TEMP_MESSAGE_SPLIT_IDX1 | 30      | NULL | 1619639 |   100.00 | Using index                                    |
|  1 | UPDATE      | t1    | NULL       | ALL   | PRIMARY,TEMP_MESSAGE_SPLIT_IDX1 | NULL                    | NULL    | NULL | 1619639 |    33.33 | Range checked for each record (index map: 0x5) |
+----+-------------+-------+------------+-------+---------------------------------+-------------------------+---------+------+---------+----------+------------------------------------------------+
2 rows in set (0.00 sec)

这个查询在temp\u message\u split表中处理1700128要花一天多的时间，我们需要调整它，使它尽可能地占用最少的时间。