def DateToWeek(year, month, day):
    # 将日期转换为星期
    if month == 1 or month == 2:
        year -= 1
        month += 12
    return (day + 2 * month + 3 * (month + 1) / 5 + year + year / 4 - year / 100 + year / 400) % 7 + 1

SELECT DAYOFWEEK(NOW()),WEEKDAY(now()),DATE_FORMAT(NOW(),"%w"),NOW()
 
 
 

 
 

 
 
now()是星期2
 
从上面结果来看。
 
DATE_FORMAT(NOW(),"%w") 2 正好对应
 
 
DAYOFWEEK(NOW())  3 大了
 
 
WEEKDAY(now()) 1 小了
 
 
 （可以理解为DAYOFWEEK长度大于WEEKDAY所以DAYOFWEEK得到为3，WEEKDAY得到为1）
 
 

 

此方法需要使用到datetime库。
 实例代码如下：
 
from datetime import datetime
week = datetime.strptime("2019-03-04","%Y-%m-%d").weekday()
print(week)
 
打印结果为0。
 该方法会返回数字0—6，依次代表周一到周日。

#include <stdio.h>
typedef enum bool{true =1,false=0}bool;
/*计算1901年之后的日期转换为星期几*/
bool yun(int year)
{
    return (year%4==0&&year%100!=0||year%400==0);
}
int datetoweek(int year,int month,int day)
{
    int n,i;
    n=365*(year-1901);
    for(i=1;i<year;i++)
    n+=yun(year);
    switch(month)
    {
    case 12:
        n=n+6*31+4*30+28;break;
    case 11:
        n=n+30*3+6*31+28;break;
    case 10:
        n=n+31*5+3*30+28;break;
    case 9:
        n=n+31*5+2*30+28;break;
    case 8:
        n=n+31*4+2*30+28;break;
    case 7:
        n=n+31*3+2*30+28;break;
    case 6:
        n=n+31*3+30+28;break;
    case 5:
        n=n+31*2+30+28;break;
    case 4:
        n=n+31*2+28;break;
    case 3:
        n=n+31+28;break;
    case 2:
        n=n+31;break;
    default:
        n=n;
    }
    if(month>2)
    n=n+yun(year)+day;
    else
    n=n+day;
    return (n%7+1); 
}

int main()
{
    printf("%d\n",yun(400));
    printf("%d\n",datetoweek(2015,2,12));
    return 0;
}