How to join two CDT's using Process Model without using MYSQL Queries??

You can try out to build a expression rule to join data from two cdts on the basis of your common field and create a datasubset out of it. Then in process model you can directly but the data from datasubset in to your third cdt, if the field of CDT and datasubset are same. Please let me know if you want anything else on this. But i think approach suggested by @sikhivahans will reduce your trouble of writing all that logic .

You can try out to build a expression rule to join data from two cdts on the basis of your common field and create a datasubset out of it. Then in process model you can directly but the data from datasubset in to your third cdt, if the field of CDT and datasubset are same. Please let me know if you want anything else on this. But i think approach suggested by @sikhivahans will reduce your trouble of writing all that logic .