如何从两个单独的列中减去时间戳，然后将此数据输入表中

Question

I am attempting to create a sign-in, sign-out program using python and mysql on a raspberry pi. I have so far successfully created a system for registering, signing in, and signing out, but am having trouble with the final component. I am trying to subtract the two separate time-stamps (signin, signout) using TIMESTAMPDIFF, and then entering this value into a separate column in the table. However, the statement I am using is not working.

Code:

employee_id = raw_input("Please enter your ID number")

minutes_calc = "INSERT INTO attendance (minutes) WHERE id = %s VALUES (TIMESTAMPDIFF(MINUTE, signin, signout))"

try:

    curs.execute(minutes_calc, (employee_id))
    db.commit()
except:

    db.rollback()
    print "Error"

Table Structure so far (apologies for formatting):

name    |    id    |    signin           |    signout          |    minutes    |

Dr_Kerbal      123     2016-08-21 22:57:25   2016-08-21 22:59:58    NULL

Please Note that I am in need of a statement that can subtract the timestamps regardless of their value instead of a statement that focuses on the specific timestamps in the example.

Additionally the datatype for the column minutes is decimal (10,0) as I initially intended for it to be in seconds (that was when I encountered other issues which have been solved since), its null status is set to YES, and the default value is NULL.

Thank You for your Assistance

Answer 1

You need an update query not INSERT

UPDATE attendance 
SET `minutes` = TIMESTAMPDIFF(MINUTE, signin, signout);