ถามเรื่อง Sum Sub Query ค่ะ ช่วยแนะนำตอนที่เอา Sum Sub Query มารวมกันหน่อยคะ

SELECT cast(StatDate as date) as VisitDate,  sum(NOBEDOCCBFW+NOBEDOCCNEW-NOBEDRETURN- NOBEDUNACKNOWLEDGE) as pretotal, 
       (SELECT sum(NOBEDOCCBFW+NOBEDOCCNEW-NOBEDRETURN- NOBEDUNACKNOWLEDGE) 
	    FROM DNHOSPITAL_TEST.dbo.HN_STAT_WARD_HEADER 
	    WHERE StatDate BETWEEN '2017-3-1' AND '2017-3-31') as total 
FROM DNHOSPITAL_TEST.dbo.HN_STAT_WARD_HEADER 
WHERE StatDate BETWEEN '2016-3-1' AND '2016-3-31' group by cast(StatDate as date);

VisitDate	     pretotal  total
2016-03-01	126	3112
2016-03-02	130	3112
2016-03-03	131	3112
2016-03-04	133	3112
2016-03-05	148	3112
2016-03-06	137	3112
2016-03-07	151	3112
2016-03-08	140	3112
2016-03-09	123	3112
2016-03-10	136	3112
2016-03-11	134	3112
2016-03-12	129	3112
2016-03-13	123	3112
2016-03-14	126	3112
2016-03-15	141	3112
2016-03-16	130	3112
2016-03-17	122	3112
2016-03-18	127	3112
2016-03-19	126	3112
2016-03-20	117	3112
2016-03-21	137	3112
2016-03-22	141	3112
2016-03-23	134	3112
2016-03-24	120	3112
2016-03-25	104	3112
2016-03-26	116	3112
2016-03-27	92	3112
2016-03-28	107	3112
2016-03-29	125	3112
2016-03-30	118	3112
2016-03-31	106	3112

SELECT cast(StatDate as date) as VisitDate, sum(NOBEDOCCBFW+NOBEDOCCNEW-NOBEDRETURN- NOBEDUNACKNOWLEDGE) as ipdinward_pretotal
FROM DNHOSPITAL_TEST.dbo.HN_STAT_WARD_HEADER 
WHERE StatDate BETWEEN '2016-3-1' AND '2016-3-31' group by cast(StatDate as date);

VisitDate	     pretotal
2016-03-01	126
2016-03-02	130
2016-03-03	131
2016-03-04	133
2016-03-05	148
2016-03-06	137
2016-03-07	151
2016-03-08	140
2016-03-09	123
2016-03-10	136
2016-03-11	134
2016-03-12	129
2016-03-13	123
2016-03-14	126
2016-03-15	141
2016-03-16	130
2016-03-17	122
2016-03-18	127
2016-03-19	126
2016-03-20	117
2016-03-21	137
2016-03-22	141
2016-03-23	134
2016-03-24	120
2016-03-25	104
2016-03-26	116
2016-03-27	92
2016-03-28	107
2016-03-29	125
2016-03-30	118
2016-03-31	106

SELECT cast(StatDate as date) as VisitDate, sum(NOBEDOCCBFW+NOBEDOCCNEW-NOBEDRETURN- NOBEDUNACKNOWLEDGE) as ipdinward_total
FROM DNHOSPITAL_TEST.dbo.HN_STAT_WARD_HEADER 
WHERE StatDate BETWEEN '2017-3-1' AND '2017-3-31' group by cast(StatDate as date);

VisitDate	      total
2017-03-01	94
2017-03-02	104
2017-03-03	108
2017-03-04	102
2017-03-05	92
2017-03-06	105
2017-03-07	108
2017-03-08	105
2017-03-09	108
2017-03-10	111
2017-03-11	110
2017-03-12	87
2017-03-13	101
2017-03-14	110
2017-03-15	122
2017-03-16	125
2017-03-17	105
2017-03-18	89
2017-03-19	71
2017-03-20	102
2017-03-21	112
2017-03-22	99
2017-03-23	93
2017-03-24	108
2017-03-25	104
2017-03-26	99
2017-03-27	90
2017-03-28	81
2017-03-29	88
2017-03-30	92
2017-03-31	87