D11—【177. 第N高的薪水】

查询 Employee 表中第 n 高的工资。如果没有第 n 个最高工资，查询结果应该为 null 。

import pandas as pd

def nth_highest_salary(employee: pd.DataFrame, N: int) -> pd.DataFrame:
    employee = employee.sort_values(by='salary',ascending=False)#降序排列
    employee = employee.drop_duplicates(subset='salary')
    if N<=0:#考虑输入N为负数
        return pd.DataFrame({f'getNthHighestSalary({N})': [None]})
    elif employee.shape[0]>=N:
        return pd.DataFrame({f"getNthHighestSalary({N})":[int(employee.iloc[N-1]['salary'])]})
    else:
        return pd.DataFrame({f'getNthHighestSalary({N})': [None]})