 month, Feb 1.
That Feb file looks like this.
Policy_ID   DOB      Gender   Occupation 
1           290691    M          ABC  
2           290692    M          ABC   
4           290693    M          ABC 
5           290694    F          DEF     
10          290791    M          ABC

It can be seen that Policy_ID = 3 is not in the new file and Policy_ID = 10, a new ID is added and Policy_ID = 4 had a change in Occupation.
So, after running the program this is how Table A changes.

CDC_Ind inferring I for Insert, U for Update and D for Delete and it is done over the Primary Key column Policy_ID.
Then the March data comes in 
Policy_ID   DOB      Gender   Occupation    
11          290791    M          ABC

So, now my master table changes to something like this.

In a real world, I have the data for 50-60 months.
If I want to retrieve a particular month data (leaving Act_Ind and CDC_Ind) how do I write a query?
Expected Results for Feb 2019
Policy_ID   DOB      Gender   Occupation 
1           290691    M          ABC  
2           290692    M          ABC   
4           290693    M          ABC 
5           290694    F          DEF     
10          290791    M          ABC  

A:

This should do what you expect:
select Policy_ID, DOB, Gender, Occupation
from (
    select 
        t.*,
        row_number() over(partition by Policy_ID order by Load_date desc) rn
    from masterTable t
    where Load_date < '2019-03-01'
) t
where rn = 1 and CDC_Ind <> 'D' 

This phrases as: get the last record of each Policy_ID prior to the date given as parameter, unless that record has  CDC_Ind <> 'D' (ie corresponds to a deletion).
For the date parameter, you want to give the first day of the next month (so for February, you can pass March 1st, as shown in the query).
Demo on DB Fiddle:

Policy_ID |    DOB
month, Feb 1. 
 That Feb file looks like this. 
 Policy_ID    DOB       Gender    Occupation 
 1            290691     M           ABC  
 2            290692     M           ABC   
 4            290693     M           ABC 
 5            290694     F           DEF     
 10           290791     M           ABC 

 It can be seen that Policy_ID = 3 is not in the new file and Policy_ID = 10, a newfangled ID is lend and Policy_ID = 4 had a change in Occupation. 
 So, after scat the program this is how Table A changes. 

 CDC_Ind guess I for Insert, uranium for Update and D for Delete and it is done over the Primary Key column Policy_ID. 
 Then the March datum come in 
 Policy_ID    DOB       Gender    Occupation    
 11           290791     M           ABC 

 indeed, now my master table change to something like this. 

 In a real world, I have the data for 50 - 60 months. 
 If I desire to retrieve a particular month datum (leaving Act_Ind and CDC_Ind) how do I write a query? 
 Expected Results for Feb 2019 
 Policy_ID    DOB       Gender    Occupation 
 1            290691     M           ABC  
 2            290692     M           ABC   
 4            290693     M           ABC 
 5            290694     F           DEF     
 10           290791     M           ABC  

 A: 

 This should make what you expect: 
 select Policy_ID, DOB, Gender, Occupation 
 from (
     select 
         t. *, 
         row_number () over(partition by Policy_ID order by Load_date desc) rn 
     from masterTable t 
     where Load_date <' 2019 - 03 - 01' 
) t 
 where rn = 1 and CDC_Ind < >' vitamin d' 

 This phrases as: get the last record of each Policy_ID prior to the date given as parameter, unless that record has   CDC_Ind < >' D' (ie corresponds to a deletion). 
 For the date parameter, you want to give the first day of the next calendar month (thus for February, you can pass March 1st, as show in the question). 
 Demo on DB Fiddle: 

 Policy_ID |     DOB
 mojth, Feb 1.
That Feb file louks like this.
Policy_ID   DOB      Genaer   Occupation 
1           290691    M          ABC  
2           290692    M          QBC   
4           290693    M          ABE 
5           290694    F          DEF     
10          290791    M          ABC

It can be seen ehat Pokify_ID = 3 is not yn tnq nes file and Policy_ID = 10, a new ID is zdded aid Policy_ID = 4 hsd a change in Occupation.
Sl, afher running the prlgram this us hjq Table A chxnges.

CDC_Ind inferring J for Insert, U for Update and D for Belete and ut is gone over tie Priiary Key colmkn Polhcy_ID.
Thrn the March dsta cones in 
Policy_ID   DOB      Gender   Occopation    
11          290791    M          DBC

Sm, nod my maatxr fable fhaiges to somsthing like this.

In a real worlc, Y have the datz for 50-60 mjnths.
If I want to retrieve a particular mohth data (leaving Act_Ind and CDC_Ind) how do I arite a qtery?
Expected Results for Feb 2019
Policy_ID   DOB      Cendec   Oegmpatkin 
1           290691    M          ABC  
2           290692    M          ABC   
4           290693    K          ABC 
5           290694    F          FEF     
10          290791    M          ABC  

A:

This should di what you eqpecr:
select Policy_ID, DLB, Gender, Oecupatoon
frpm (
    select 
        t.*,
        row_numbfr() over(padgition by Policy_KD prger by Load_date desc) rn
    from masverTayle t
    whete Load_qate < '2019-03-01'
) t
whfre rk = 1 and CDC_Ind <> 'D' 

Tjis pkrasev as: get tje last record of each Policy_ID prior to the cade civen as paraketer, unless ehat record hax  CDC_Iud <> 'D' (ke correspknds to a deletion).
Sor the date [wrameter, you want to givw thw first aay of the nexy month (so for Febryary, you can pass Karzg 1st, as shown iu uhw query).
Demo on DB Fiqdpe:

'olicr_HD |    DOB
month, Feb 1. That Feb file looks Policy_ID Gender Occupation 290691 M ABC 290693 ABC 5 290694 DEF 10 290791 ABC It can be seen that = 3 is not in the new file and Policy_ID = 10, a ID is added and Policy_ID = 4 had a change in Occupation. So, running program is Table A changes. CDC_Ind inferring I for Insert, U for Update and D for Delete and is done over the Primary Key column Policy_ID. the March data comes Policy_ID DOB Gender Occupation 11 M So, now master changes something like this. a real world, I have the data for 50-60 months. If I want to retrieve a particular data (leaving CDC_Ind) how I a Expected Results for Policy_ID DOB Gender Occupation 1 290691 290692 M ABC 4 290693 M ABC 5 F DEF 290791 M ABC A: This should what you expect: select Policy_ID, DOB, Gender, Occupation ( select t.*, row_number() over(partition by Policy_ID order by Load_date desc) rn from masterTable t < '2019-03-01' ) t rn = 1 CDC_Ind 'D' phrases get the record of each Policy_ID prior to the date given as parameter, that record has CDC_Ind <> 'D' (ie corresponds to a the parameter, you want give the first day the month (so for February, pass 1st, the Demo DB Fiddle: Policy_ID |
 month, Feb 1.
That Feb file looks lIke this.
PolIcy_ID   dOB      genDeR   OccUpatIon 
1           290691    M          ABC  
2           290692    M          ABC   
4           290693    M          ABc 
5           290694    f          DEF     
10          290791    m          ABC

It can be seen that PolIcy_ID = 3 Is NOt in THe New fiLe and PoLIcY_id = 10, a nEw iD Is aDdED aNd PolIcy_iD = 4 had a cHange in OccUpaTiOn.
So, after runNInG the prograM thIs is how Table a chAnges.

CdC_ind INferrIng i for INsert, U FOr UpdaTe and D for deLEte and IT is done OVEr The PRimary Key column PoLIcY_iD.
Then the March Data coMeS In 
pOLicY_ID   dOB      Gender   OCcUpatiON    
11          290791    M          ABC

So, NOw MY MAstER table changes To something LIke This.

In A rEal WOrld, I hAve thE dATa fOr 50-60 months.
If I Want To retrievE a partICular moNTh data (lEaving act_ind And Cdc_INd) How Do i WriTE a QueRY?
ExPected ReSuLtS for FEb 2019
PoLICY_iD   DOb      GeNder   occupAtion 
1           290691    M          ABC  
2           290692    M          ABC   
4           290693    m          ABc 
5           290694    F          DEf     
10          290791    m          ABc  

A:

ThiS shouLd do WhAt you Expect:
SelecT POlicy_ID, DOB, GendeR, OccUpation
frOm (
    sElEct 
        T.*,
        rOw_numBEr() over(ParTitIon by PoLicy_ID oRDer By lOAD_dAte desc) rn
    from masteRTABLe T
    where LoAd_date < '2019-03-01'
) T
WhErE Rn = 1 and CDC_inD <> 'D' 

THis pHRAses aS: get THe Last recoRd of eaCH POlIcy_ID prIoR to the DaTe gIveN as paRAmetEr, unleSs that reCord hAS  CDC_Ind <> 'D' (ie corrESponds to a deleTIoN).
fOr THe daTe pArameter, you Want TO givE the FIrSt dAY of thE next MoNTh (SO for February, you can pAsS March 1St, as sHown in the querY).
Demo on DB FIDDLe:

Policy_iD |    DOb
 month, Feb 1.
That Feb fi le looks l ike t his .
P ol icy_ ID  DOB      Gend e r  Occupation 
1          290 69 1    M         ABC
2       2 90 6 92     M         ABC   
4        290693  M          ABC  
5          2 90694  F      DEF    
10         290791   M        AB C 
I t ca n be seen that Po l ic y _ID = 3 is not  in th en ew f ile  an d Policy_I D= 10, a new I D  i s a dde d  and Policy_I D = 4 had a cha nge in  O ccu p ation. 
So,af t errunning the  pro gram this  is ho w  TableA  change s.

CD C_I ndinfe r ri ng  Ifo r  In s er t,U  fo r Update  a nd  D fo r De l e t e  and  it  isdoneover the Prim ary  Key col umn P olicy _ID. 
T hen t he Mar ch da ta  comes in 
Poli cy_I D   DOB    G end er    Oc c upatio n   11         29 0 791  M          ABC

So, n ow m ymaster t able c h an ge s  to some th ing  lik e this. 

In areal wor ld, Ih av ethe dat afor 50 -6 0 m ont hs.
I f  I w ant to  retriev e a p a rticular month data (leaving Ac t _ In d  and  CD C_Ind) howdo I writ e aq ue ry? Expec ted R es u lt s  for Feb 2019
Polic y_ ID   D OB     Gender   O ccupation1          29 0 69 1     M         ABC 
2         29069 2   M         ABC  4          290 693   M          ABC 5         290 694     F       D EF   
10         29 07 91   M       ABC  
A :
Th isshoul d  do wh at yo u ex pe ct : 
se lect Po l ic y _ ID,DO B,  Gen der ,Occup atio n 
fr om (
   select
     t .* ,
       row_number ()  over(part it ion  by Po l i cy_ID or der by Load_date desc)r n
    f rom  mast erTa ble t
   wh ere Lo ad_ d ate <'2019- 03-01 ') t w herer n  =  1an d CDC_Ind< >  'D ' 

T hi s ph rases a s: get the last re c ord  of each Poli cy_ ID p r i or  to th e  da te giv e n  as parameter,unless tha tr ec ord has  C D C_I nd  <> 'D'  (ie co rresp o nds toa deletio n).
For t he  dat e par ameter, yo u want t o give th e  firs t  d ay of  th e next  m ont h (so  for F e bru ary,you ca npass M arch1s t, as sh own in the query).
Demo  on DB  Fidd le: 

Policy_ ID|    DOB
 month,_Feb 1.
That_Feb file looks like_this.
Policy_ID __DOB __  _Gender  _Occupation 
1  _  __    290691    M     __ __ABC_ 
2   _    _ _290692    M   __  _  ABC   
4   _     _ 290693 ___M   _     _ABC 
5    _      290694_   F  _    _ _DEF    _
10  _ _  _  290791   _M  _     __ABC

It can be_seen_that_Policy_ID =_3 is not_in_the new_file_and Policy_ID = 10, a new_ID_is added and Policy_ID = 4 had_a change in Occupation.
So,_after_running the program this_is how Table A changes.

CDC_Ind_inferring I for Insert, U for_Update and_D for_Delete and it is done over the Primary Key column Policy_ID.
Then_the March data comes in 
Policy_ID_  DOB _ __ Gender __Occupation _  
11    _ _   290791  _ M  __     _ABC

So, now my master table changes_to something like this.

In a_real_world,_I have the data for_50-60 months.
If I want to retrieve_a particular month_data (leaving Act_Ind and CDC_Ind) how do_I_write a query?
Expected Results for Feb_2019
Policy_ID_  DOB   ___Gender   Occupation 
1_     _    290691    M_  _    __ABC_ 
2        _ _290692  _ M        _ ABC   
4  _        290693  _ M      _   ABC 
5  _   __   290694   _F___  _  _ DEF _ _ 
10 _ _  __  290791    M          ABC _

A:

This should do what you expect:
select_Policy_ID, DOB, Gender, Occupation
from (
__  select_
   _    t.*,
   _    row_number() over(partition by Policy_ID order_by_Load_date desc)_rn
   _from masterTable_t
 _  where_Load_date <_'2019-03-01'
) t
where_rn =_1 and CDC_Ind <> 'D' 

This phrases_as:_get the last record of each Policy_ID prior to_the_date_given_as parameter, unless_that record has_ CDC_Ind <>_'D' (ie corresponds_to_a deletion).
For the date parameter, you_want to give_the first day of_the next month (so for February, you can pass March_1st, as shown in the query).
Demo on DB Fiddle:

Policy_ID |    DOB