小编Ame*_*ain的帖子

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
    SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT N-1,1
);
END

当M = 0变为-1时，该查询会给出异常，但是当我这样写时

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
DECLARE M INT;
SET M=N-1;
  RETURN (
    SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT M,1
);
END

请解释这两个语句之间的区别。当我设置M = N-1时，当N = 0时m也会为负，因此出现以下异常

Line 6: SyntaxError: near '-1,1
);
END'