How I check existing record and avoid redundant data - sql

Question

I have two tables, both are situated at different server and belongs to different schema.
Table 1 : SALARY_DETAIL_REPORT_[monthYearSuffix]-Same Replica of Table 2.
Table 2: XXMPCD_SALARY_DETAIL_TABLE-Contains employee's salary related data,each employee having multiple pay code like HOUSE RENT ALLOW,DEARNESS ALLOW, NPS-Company Contri(Earning), BASIC PAY, NET EARNING, GROSS DEDUCTION, GROSS EARNING, GROSS DEDUCTION, NET EARNING, BASIC PAY, GRADE PAY.
So Employee code repeated multiple times and hence we are not able to maintain primary key or unique index.
Suppose 1000 records pushed in TABLE 2 which I need to copy exactly in my TABLE 1. This is handle by my SPRING service class a GUI is available in which we simply click on migrate button and services running in background fetch the data from TABLE 2 and insert the same in the TABLE 1.
There is two column inside TABLE 2
1.PICK_DATE
2.IS_DATA_PICKED
If both of these data contain null that simply means that data is not migrated into our TABLE 1, we updated the same columns after successful migration by acknowledging, so the next time the data will not be available for migration.
PROBLEM
Now suppose we migrated the 1000 records from TABLE 2 to TABLE 1.
What I done, I go back to my SQL DEVELOPER, choose 3 random records and set their PICK_DATE & IS_DATA_PICKED to NULL.
Now I migrated the same another time and those 3 records inserted again.
That means replication of 3 records, 1000 records becomes 1003.
Now what I want to check:
If same data existed, than record should be updated not inserted, means overwrite.
TABLE 1:SALARY_DETAIL_REPORT_092018
SALARY_REPORT_ID
EMP_NAME
EMP_CODE
PAY_CODE
PAY_CODE_NAME
AMOUNT
PAY_MODE
PAY_CODE_DESC
YYYYMM
REMARK
EMP_ID
PRAN_NUMBER
PF_NUMBER
PRAN_NO
ATTOFF_EMPCODE
REFERENCE_ID
**
TABLE 2:XXMPCD_SALARY_DETAIL_TABLE
EMP_NAME
EMP_CODE
PAY_CODE
AMOUNT
PAY_MODE
PAY_CODE_NAME
YYYYMM
REMARK
PUSH_DATE
PICK_DATE
IS_DATA_PICKED
ERROR_MESG
REFERENCE_ID
PRAYAS_ERP_ORG_ID
ERP_ORG_ID
PF_NUM
PRAN_NO
VERIFIED_BY