Another method: You may also use case when

Select case
when exists(select * from tb_user where user_id=1)
then 'Ok'
else 'Not'
end
;
 

Another method: You may also use case when

Select case
when exists(select * from tb_user where user_id=1)
then 'Ok'
else 'Not'
end
;
 

• SQLFiddle Demo

Sample table:

ID  NAME
1   john
2   tim
3   jack
4   rose

Query: renamed the columns as Status

Select case
when exists(select * from table1 where id=1)
then 'Ok'
else 'Not'
end as Status
;

Results:

STATUS
Ok