mysql - SQL UNION ALL for a single result -

i have 2 tables, example student table , student_history table. both student , student_hostory tables contain same number of columns. if student in history table wont in student table.(one index number a0001 can in 1 table either student or student_history)

if want student details index number, have 'union all' both tables , find user.

is there easy way done, other union all. since result set contain 1 row either in student or student_history table.