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Message Posted: Thu, 16 May 2002 @ 18:11:17 GMT
Subj:   Re: Rounding in Teradata 

From:   Buckland 
Teradata follows the IEEE standard for rounding, which is exactly what you laid out. If the number next to the 5 is even it rounds down.
If it is odd it rounds up. Or restating "the 5 rounds to the closest even number".
Here's the reason for that  It keeps the sum from getting a systematic error. Many people think that any '5' should round up (or
down). If anything that ends in 5 rounds up then the sum of a large list will have a slight upward bias. Essentially 1,2,3,4 would round
down and 5,6,7,8,9 would round up (numbers ending in 0 don't round). So the sum of large column of these rounded numbers would likely be
slightly larger than the actual sum of the non rounded numbers.
By dividing the numbers ending in 5 (half up, half down) the errors introduced by rounding cancel themselves out. Therefore a large sum
of these numbers won't have an upward (or downward) bias. If you change how things round be sure that a slight upward bias of the rounded
numbers isn't important.
Mike Buckland
 