If this is the XY problem I think it is, you could get Sybase to split the dateparts for you in advance using the Transact-SQL datepart function, e.g.:

SELECT datepart(yy,attr_val),
       datepart(mm,attr_val),
       datepart(dd,attr_val)
FROM date_attribute_values
WHERE instrument_id = 12345
AND attr_id = 'MATURITY'
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