I wouldn't do that. It's against the "Rules" of normalization. You don't want to make a row dependant on another row in the same table. Think of all the fuzz to update the table when you find out someone inserted some wrong data last year, or when HR decides to change the rules (quite probable actually). So you should make a query that gets you the result you want instead. Hint, checkout ROLLUP. For example:
SELECT EmpID,
CASE WHEN (GROUPING(Leave_Year) = 1) THEN 'Total Balance'
ELSE ISNULL(Leave_Year, 'UNKNOWN')
END AS Leave_Year,
SUM(Balance) AS Balance
FROM MyTable
GROUP BY EmpID, Leave_Year WITH ROLLUP
I haven't tested this code, but it should give you an idea. I also assumed SQLServer, Different Databases have different syntax. Use Google.
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