MySQL 5.6

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create table emp_master(token_no int, vehicle_no int);
insert into emp_master (token_no, vehicle_no) 
select token_no, vehicle_no
from (
select 1234 token_no, 12345 vehicle_no
) rec
where not exists (select * from emp_master where vehicle_no = rec.vehicle_no);

Records: 1  Duplicates: 0  Warnings: 0


insert into emp_master (token_no, vehicle_no) 
select token_no, vehicle_no
from (
select 1234 token_no, 12345 vehicle_no
) rec
where not exists (select * from emp_master where vehicle_no = rec.vehicle_no);

Records: 0  Duplicates: 0  Warnings: 0


select * from emp_master;


token_no
vehicle_no


1234
12345