Re: UPDATE sql question
От | Ron Johnson |
---|---|
Тема | Re: UPDATE sql question |
Дата | |
Msg-id | 1059753264.7508.612.camel@haggis обсуждение исходный текст |
Ответ на | Re: UPDATE sql question (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: UPDATE sql question
|
Список | pgsql-general |
On Fri, 2003-08-01 at 10:16, Tom Lane wrote: > Ron Johnson <ron.l.johnson@cox.net> writes: > > On Mon, 2003-07-28 at 03:24, Andrei Verovski wrote: > >> What exactly will happen if UPDATE sql statement instructs to update > >> some columns with the same values as already in the database? Will > >> Postgres update only different values or it will simply modify all > >> columns listed in UPDATE sql? > > > Looks like it does what you tell it to do... > > I think he was asking an implementation question, viz: does it skip the > physical update if no values in a row actually change? The answer is > no. I'd think that in most cases, the extra time spent checking to see > whether the updated columns didn't change would be a net loss. Would it always be a net loss, though? If *none* of the fields were updated, then you could burn some CPU (doing comparisons) to save a disk write. CPUs are so fast, nowadays. How many microseconds *would* be spent? Of course, one could always say, "Hey, application! Don't update unchanged values!!!!". -- +-----------------------------------------------------------------+ | Ron Johnson, Jr. Home: ron.l.johnson@cox.net | | Jefferson, LA USA | | | | "I'm not a vegetarian because I love animals, I'm a vegetarian | | because I hate vegetables!" | | unknown | +-----------------------------------------------------------------+
В списке pgsql-general по дате отправления: