SQL Best Practices - Part1

Never put SQL scalar functions on columns in the WHERE predicates.
For example: WHERE YEAR(HIREDATE) = 2009 should be recoded as WHERE HIREDATE BETWEEN '2009-01-01'and '2009-12-31'.
When placing SQL scalar functions on columns in the SELECT portion of the SQL statement does incur some minimal overhead, but applying it to a column in the WHERE clause causes the predicate to become stage to non indexable.

Same applies for mathematics.
For example: WHERE HIREDATE – 7 DAYS > :HV-DATE should be recoded as WHERE HIREDATE > :HV_DATE + 7 days. Having the mathematics on the host variable is not a problem.