下面是一个解决问题的方法：

res = a.join(b.assign(name='Mr. ' + b['first name'] + ' ' + b['last name']).set_index('name'), on='name')

输入：

dataframe a:
             name designation
0  Mr. james john     manager
1   Mr. jim james      tester
2   Mr. abe james   developer

dataframe b:
  first name last name  emp id
0      james      john       1
1        jim     james       2
2        abe     james       3

输出：

name designation first name last name  emp id
0  Mr. james john     manager      james      john       1
1   Mr. jim james      tester        jim     james       2
2   Mr. abe james   developer        abe     james       3