Merging table along with update a column which has comma sepated string

Question

i have a table1 Option

  ID  |option  | PreRequisite
 -------------------------------------
   1  | India  | null      
   2  | Japan  | null
   3  | China  | null 
   4  | ABC    | Q1|1,Q2|2
   5  | DEF    | Q1|1
   6  | KLM    | Q1|1

i have another table2

  Key | ParentOption |ChildOption
 ---------------------------------
   Q1 | INDIA        | EFG
   Q1 | INDIA        | GHI
   Q1 | JAPAN        | ABC
   Q1 | JAPAN        | DEF
   Q1 | INDIA        | KLM

so i have to merge this 2 tables and which ever child option is not present in table1 ,i have to insert that childoption along with PreRequisite updated to Q1|"ID of parent from the table 1" i.e for "Q1 | India | EFG " the new entry in table 1 should be

ID | option|  PreRequisite
----------------------------
 7 |  EFG   | Q1|1

now if the childoption is already there in table1 ,i have to append the parentoption's id from table1 into prerequisite column .

i.e for Q1 | JAPAN | DEF row should get update to

ID  |option  | PreRequisite
-------------------------------------
 1  | DEF   | Q1|1|2

for Q1 | JAPAN | ABC row should get update to

ID  |option  | PreRequisite
-------------------------------------
4  | ABC    | Q1|1|2,Q2|2

but for childoption which are already there in the table along with prerequisite filled with Q1|"parentOption's id",nothing should be updated.

for Q1 | INDIA | KLM row should get update to

ID  |option  | PreRequisite
-------------------------------------
5  | KLM     | Q1|1

so the final result should be

  ID  |option  | PreRequisite
 -------------------------------------
   1  | India  | null      
   2  | Japan  | null
   3  | China  | null 
   4  | ABC    | Q1|1|2,Q2|2
   5  | DEF    | Q1|1|2
   6  | KLM    | Q1|1
   7  | EFG    | Q1|1
   8  | GHI    | Q1|1