| Subject | Re: [firebird-support] Float v. Double |
|---|---|
| Author | Helen Borrie |
| Post date | 2010-09-22T01:52:46Z |
At 12:32 PM 22/09/2010, you wrote:
Be aware, though, of the unreliability of the existing data, compared to any new data that is stored after the type change. When it was stored as FLOAT, you had 9 digits of precision of which (at most) 7 would be reliable. There is no way to "squeeze" more exactness from the same data, i.e., no casting or calculation that would enhance the exactness to ~ 15 digits that you would expect with data stored to the same columns as DOUBLE PRECISION. So those older data will remain roughly as [in]accurate as they always were.
./heLen
>If I need to alter a table field from float to double,No...but the FLOAT values are compatible with the new data type of the column.
>does the data get converted at the time of the alter
>or do I need to export/import the data to get the correct values?For some type alterations you would need to, but for this one, no, there is nothing more to do.
Be aware, though, of the unreliability of the existing data, compared to any new data that is stored after the type change. When it was stored as FLOAT, you had 9 digits of precision of which (at most) 7 would be reliable. There is no way to "squeeze" more exactness from the same data, i.e., no casting or calculation that would enhance the exactness to ~ 15 digits that you would expect with data stored to the same columns as DOUBLE PRECISION. So those older data will remain roughly as [in]accurate as they always were.
./heLen