I have an employee_ref_id column and can have multiple entry in address table. When employee do any chnage a new row insert in address table and new row in employee table. I have to count how many times he changed his address.
Example: employee : JOHN
employee_ref_id in year 2017 is : 100
with this id, he have an address in address table suppose "Newyork"
after that in 2018 he changed address 4 times
for same employee john , 4 ref_id created 101, 102,103,104
address : washington, newyork, newyork, washington
basically he chnaged 3 times.since 2017. first newyork to washington and then washinton to newyork and in last again newyork to washington.. so I have to give count 3.