leave balance

hi,

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i have a table called emp-leave_balanced(leave-id,leave balance,etc are column),in leave balance column each employee has some leave balance (like 4,5,8 etc)i need to add this leave-balance to another column(that also have common value like 25) i need to update this new column based on system time at the end of 31st December at 12.00am.>>>>>

ok so how will i update the new column that column already have value 24 and all employee have some leave balance how to add all this can u tell me for one or two leavebalance some pseudo code example