>>Hear is my SELECT statement:
>>SELECT some_number AS mynumber FROM mytable
>>
>>the data type of mynumber is 20.8 and I would like it to be 8.4.
>>any ideas?
>
>sele round(some_number,4) as mynumber from mytable
>
>This will give you four decimal places but I'm not sure how or if you can change from 20 digites right of the decimal to 8.

I should've said ...

...but I'm not sure how or if you can change from 20 digites right of the decimal to 8 ... without changes to underlying data structure.