joins in ppython using join code example

Example 1: SQL joins in python

This was What I intended
 ID Case NxtCase
 1    A        
 2    C        
 3    E      

This is my desired result

 ID Case NxtCase
 1    A        B
 2    C        D
 3    E        F

Example 2: what is join use for in python

>>> sentence = ['this','is','a','sentence']
>>> '-'.join(sentence)
'this-is-a-sentence'