Mysql查询以一个缺失的id

@i声明变量；id自增长，由于删除而id不连续，查询缺失id (id范围1至65535)

SELECT id-1  FROM 
(	
SELECT (@i:=@i+1)  i, t1.id FROM test_table t1,(select   @i:=0) it
WHERE cast(t1.id as DECIMAL) <= '65535' 
AND cast(t1.id as DECIMAL) >= '1'
ORDER BY t1.id ASC
) t2
WHERE i != id
LIMIT 1;