MySQL连表查询datetime字段索引失效

[精彩呢]

求助！
A表：

create table if not exists V_MEDICAL_INCOME
(
	areacode varchar(16) null,
	areaname varchar(32) null,
	APPLYDEPARTMENTCODE varchar(16) null,
	APPLYDEPARTMENTNAME varchar(32) null,
	EXECUTIONDEPARTMENTCODE varchar(16) null,
	EXECUTIONDEPARTMENTNAME varchar(32) null,
	EXECUTIONDEPARTMENTTYPE varchar(4) null,
	OUTPATIENT varchar(4) null,
	CHARGEID varchar(16) null,
	TYPE varchar(32) null,
	DRUGCODE varchar(32) null,
	INCOME decimal(16,2) null,
	PAYMENTROUTE varchar(16) null,
	CHARGEAT datetime null,
	RJSJ datetime null,
	RJSH int null,
	SFYID varchar(16) null,
	PATIENT_NO varchar(16) null
)
comment '视图-收入明细';

create index V_MEDICAL_INCOME_INDEX
	on V_MEDICAL_INCOME (CHARGEAT);

create index V_MEDICAL_INCOME_INDEX_RJSH
	on V_MEDICAL_INCOME (RJSH);

B表：

create table if not exists V_INCOME_RJSH
(
	opercode varchar(16) null,
	checkflag varchar(4) null,
	checkdate datetime null,
	begindate datetime null,
	enddate datetime null
)
comment '视图-日结审核';

create index V_INCOME_RJSH_INDEX
	on V_INCOME_RJSH (checkdate);

create index idx_opercode
	on V_INCOME_RJSH (opercode);

执行计划：

EXPLAIN 
SELECT max(m.areaCode)       AS area_code,
       m.areaName            AS area_name,
       max(m.departmentCode) AS department_code,
       m.departmentName      AS department_name,
       sum(m.income)         AS income,
       CASE m.type
           WHEN '卫材' THEN 1
           WHEN '化验费' THEN 1
           WHEN '检查费' THEN 1
           WHEN '西药' THEN 1
           WHEN '中成药' THEN 1
           WHEN '中草药费' THEN 1
           WHEN '外送项目' THEN 1
           ELSE 2 END        AS service
FROM (
         SELECT t.INCOME                         AS income,
                t.APPLYDEPARTMENTCODE            AS departmentCode,
                t.APPLYDEPARTMENTNAME            AS departmentName,
                cast(t.AREACODE AS UNSIGNED INT) AS areaCode,
                t.AREANAME                       AS areaName,
                t.TYPE                           AS type
         FROM V_MEDICAL_INCOME t,
              (SELECT DISTINCT tt.OPERCODE, tt.BEGINDATE, tt.ENDDATE, tt.CHECKDATE
               FROM V_INCOME_RJSH tt
               WHERE tt.CHECKFLAG = 2
                 AND tt.CHECKDATE BETWEEN '2019-05-01 00:00:00' AND '2019-05-01 23:59:59') ff
         WHERE t.OUTPATIENT = 1
           AND t.TYPE != '挂号费'
           AND t.CHARGEAT >= ff.BEGINDATE
           AND t.CHARGEAT >= ff.ENDDATE
           AND t.sfyid = ff.opercode
     ) m
GROUP BY areaName, departmentName, type

EXPLAN查看执行计划如下：



从执行计划可以看到t.CHARGEAT字段是没有走索引的，查一天的数据要花几分钟，如果把查询条件改成：

AND t.CHARGEAT BETWEEN '2019-05-01 00:00:00' AND '2019-05-01 23:59:59'

就会走V_MEDICAL_INCOME_INDEX索引，效率提高百倍，求教大神能帮忙看一下为什么V_MEDICAL_INCOME表不走索引吗？
排除条件查询的数据大于全表数据的30%，t.CHARGEAT和ff.BEGINDATE都是datetime类型。
V_MEDICAL_INCOME表有一亿条数据，V_INCOME_RJSH有300来万条。

[卖水果的net]

如果把查询条件改成： 不等价了，所以比较两个的性能，价值不大。 尝试一下： (SELECT DISTINCT tt.OPERCODE, tt.BEGINDATE, tt.ENDDATE, tt.CHECKDATE FROM V_INCOME_RJSH tt WHERE tt.CHECKFLAG = 2 AND tt.CHECKDATE BETWEEN '2019-05-01 00:00:00' AND '2019-05-01 23:59:59') ff 这一堆，先写到一个临时表， 并在 OPERCODE 建立索引。