如何编写这样的MySQL语句？

create table test(
  id ...
  weight ..
);

recordN.weight >=(recordN-1).weight+1

select weight from test where id = (select MAX(id) from test);

if (newWeight >= weight)
{
   //insert here
}

SELECT weight FROM test ORDER BY id DESC LIMIT 1 INTO @weight;
INSERT INTO test (weight) VALUES (@weight+1);

INSERT INTO test (weight) SELECT (weight+1) FROM test ORDER BY id DESC LIMIT 1;